Computer Won't Turn On: What to Check First (2026)

By LK Wood IV · 2026-09-28 · ~10 min read · St. Louis County, MO

Two different faults hide behind “my computer won’t turn on.” In one, nothing happens at all when you press the button. In the other, the fans kick for a second and everything stops. They share the first few minutes of checks and then split, so it pays to know which one you have before you open anything.

This page is for a desktop that will not start. If yours powers on with the fans running and the screen stays black, that is a display or POST fault, and my graphics card not detected guide starts from there.

Match what the PC does to where the fault is

The last row is easy to miss. A press normally wakes a sleeping PC, and on the board in my desktop ASUS’s manual says the power LED blinks in sleep. A machine that ignores the press may be hung while still running, and for a running system the ACPI specification defines holding the power button for four seconds or longer as an override that sends it to soft-off, so the next press is a clean start.

Outside the case first

None of this needs tools. All of it together takes about a minute.

1. Plug a lamp or a phone charger into the same wall outlet. Intel’s troubleshooting guide starts here, with a device you know works.
2. Take the power strip or UPS out of the chain and plug the PC straight into the wall.
3. Check the rocker switch on the back of the power supply. I is on and O is off, and a moved tower can knock it to O.
4. Reseat the power cord at both ends. Many monitors use the same cord, so Intel suggests swapping the monitor’s cord onto the PC as a test.
5. Unplug everything else from the back: USB devices, display cables, the lot. Intel notes that USB devices and display cables occasionally cause power problems.

Then drain it. Pull the cord from the power supply, hold the case power button for 15 to 20 seconds, plug back in, set the rear switch to I and press power once. That hold is Dell’s desktop step for discharging residual power, and it costs nothing.

Look for a light on the motherboard

With the supply plugged in and its switch on, look at the board through the side panel before you press anything. Any lit LED there is good news.

A power supply keeps one small output alive whenever it has AC power, the +5VSB rail, and Intel’s ATX design guide says the signal that turns the PC on has no effect on it, so a light on the board means the outlet, the cord and the supply’s standby side all work and the fault sits somewhere between the button and the supply’s main outputs. Intel’s guide names the case button and its wires as a potential culprit there.

The board in my desktop is an ASUS ROG STRIX B650-A Gaming WiFi, and ASUS’s manual for it names two lights worth knowing. The case power LED on that board’s header “lights up when the system is connected to a power source”, so a glowing power LED with the PC off means standby is there. A second LED, marked PLUG_8PIN_PWR, “lights up to indicate that the 8-pin power plug is not connected.” If that one is lit, plug in the CPU power cable before anything else.

No light proves nothing. Plenty of boards have no standby LED, so carry on either way.

Start it with a screwdriver

This is the test that splits a dead button from a dead power supply or board. I would never skip it. If the PC is a prebuilt still under warranty, stop first: Intel’s guide warns that opening one can violate the warranty and suggests asking the system maker.

The case power button does very little. It connects two pins on the motherboard’s front-panel header for a moment. The board then pulls the supply’s PS_ON# line low, which Intel’s ATX guide defines as the signal “that allows a motherboard to remotely control the power supply”, and the supply turns on its main outputs. You can make the button’s momentary connection yourself.

1. Leave the PC plugged in with the rear switch on, and leave the 24-pin and CPU power cables connected.
2. Find the front-panel header in the motherboard manual. The two power pins carry a label like PWR_SW or PWRSW. On my B650-A, ASUS labels the pair PWRBTN# and GND.
3. Pull the case’s power-button plug off those two pins.
4. Touch the tip of a metal screwdriver across both pins at once, briefly.

Intel’s guide says the system will turn on “if everything is connected correctly.” Touch only the two pins the manual names. Some boards also have a power button soldered on, and Intel says pressing it does the same job.

What happens next decides the rest of the page:

• It starts. The board and the power supply work. The case button or its lead has failed; go to the button section.
• Nothing at all. The button is cleared and the fault is in the power path; go to the power path.
• A twitch, then off. Go to twitch and die.

The button or its lead

The repair costs nothing if the case has a reset button. Intel’s guide says the reset and power switches “operate in the same way”, so move the case’s reset plug onto the power pins and the reset button becomes the power button. You lose the reset function. On my B650-A the reset pair sits in the same header, labeled RSTCON# and Ground.

Look at the lead itself before you settle for that. A plug that slid half off one pin, or a wire broken where it enters the plug, gives exactly this symptom, and reseating or replacing that lead is the whole repair. A button that feels stuck or gritty has a mechanical fault in the switch itself, and for a failed case button Intel’s advice is to ask the case maker for the long-term fix.

Follow the power back to the PSU

If the screwdriver did nothing, the board never got power or never passed the signal on, so the next stop is the two cables that carry both and the supply behind them. Unplug the PC from the wall before you touch a cable.

Reseat both motherboard power cables, the wide 24-pin and the 8-pin CPU cable, until each latch clicks. On a modular unit, reseat both ends. Some boards carry a second CPU power socket — a 4-pin or another 8-pin — and ASUS’s no-power FAQ recommends filling every one the board has, while the manual for my B650-A asks for the 8-pin alone or the 8-pin and the 4-pin together.

The 24-pin matters more than it looks, because the power-on signal travels through it. PS_ON# is pin 16, the green wire. Intel’s design guide says that when PS_ON# is open-circuited the main outputs stay at zero, so a pin that never makes contact leaves the board with no way to start the supply.

Test the power supply on its own

My PSU failure symptoms guide calls the paperclip test limited, and for a PC that crashes under load it is. Here it answers the exact question you have: can the supply switch on at all?

1. Switch the supply off at the rear and pull the cord.
2. Unplug every supply cable from the parts, the 24-pin included.
3. Bridge the green wire’s socket (pin 16, PS_ON#) to any black wire’s socket, which is ground, with a bent paperclip.
4. Plug in and switch on.

A supply that starts spins its fan, with one catch. Many current units run a zero-RPM fan mode, and Corsair describes the fan as “completely off when it is not needed”, so a still fan on a quiet unit proves nothing. On those, set a multimeter to DC volts and read a yellow wire, which is +12 V, against a black one at the back of the connector. About 12 V means the supply switched on. Switch off at the rear and pull the cord before you remove the paperclip or move a probe.

Some Dell desktop supplies skip the paperclip entirely. They carry a built-in self-test button, and Dell says the supply works if its LED lights when you press it.

If the supply fails the paperclip test on a known-good outlet and cord, it is dead. Replace it or claim the warranty. If you have a spare supply you trust, Intel’s version of the test is to connect only its 24-pin and CPU cables to the board and press power; if the PC starts, the old supply was the fault.

If the supply passes and the board still will not start from the screwdriver with both cables seated, the board or the CPU is what is left. Telling those two apart takes a spare of one of them.

If it twitches and dies

A twitch means the supply started and then shut itself down, and a tripped protection is the first suspect. Corsair’s explainer says short-circuit protection shuts the supply down “should the 3.3V, 5V, and 12V rails short to any other rail, or to ground”, and its over-power protection trips at 115 to 135 percent of rated output.

After a trip, Intel’s ATX guide says the supply returns to normal only once the fault has been removed and its on signal has been off for at least one second. Pressing again gives you the same twitch for as long as the fault is there. So stop pressing and go looking.

Look for a short first. Intel names two: a motherboard screwed to the case without the standoffs it needs, and stray Molex pins touching the chassis. After a new build, those two and anything metal loose in the case are where I would look.

Then strip the machine to the minimum Intel describes. Pull the graphics card, disconnect every drive including M.2 SSDs, unplug everything from the I/O ports, and leave one stick of RAM in the slot your manual names for a single module (DIMM_A2 on my B650-A). If it now stays on, add parts back one at a time, powering down between each, until the twitch returns. The last part you added is the suspect.

You do not need a picture for this. The only question is whether it stays on with the fans running.

If it still twitches stripped to board, CPU and one stick of memory, with nothing shorting, the fault is the board, the CPU or the supply. A known-good supply is the cheapest of the three to borrow, so test that first.

On a laptop

A laptop gives you less to reach.

• Try a known-good charger if you have one, and check the charger’s light.
• If the battery is removable, take it out and try on AC power alone. Dell’s no-power steps include this one.
• Do a power reset. HP’s version is to shut down, disconnect the charger and any nonessential devices, hold the power button for about 15 seconds, then reconnect and start.
• Some Dell laptops support a real-time clock reset: with the charger connected, hold power for 30 to 35 seconds until the power light blinks three times. Dell says it aborts under 25 seconds or over 40, and that it resets the BIOS settings, date and time.

Past that, a laptop showing no sign of power is a repair or warranty job.

What not to do

• Never plug modular cables from your old power supply into a new one. Corsair’s guidance is to “never try to use one brand’s cables with another brand’s PSU”, because each maker wires the PSU end its own way, and even within one brand the cable type has to match.
• Do not short pins you have not identified. On my B650-A, ASUS warns that shorting or jumpering the clear-CMOS header, CLRTC, outside of a CMOS clear “will cause system boot failure.” Read the label before the screwdriver touches anything.
• Keep the power supply’s case closed. It can hold a dangerous charge after it is unplugged, which my PSU guide covers in its safety section.
• A pop, a spark or a burning smell ends the diagnosis. Unplug the PC and leave it off.
• Ignore generic beep-code charts. Intel’s guide points out that every motherboard maker uses its own codes, so read your board’s manual.

When to stop and send it back

• A supply that will not start on the paperclip test, on a known-good outlet and cord, is finished. Replace it or claim its warranty.
• A board that will not start from the screwdriver with a known-good supply, both power cables seated, nothing shorting and the machine stripped to CPU and one stick of memory has failed, or its CPU has. That is warranty work for one of the two, and a shop with a spare of either can tell you which.
• A prebuilt still under warranty goes back to its maker before you open the case.