Monitor Says No Signal? Find Where Your PC Stops (2026)

By LK Wood IV · 2026-09-29 · ~10 min read · St. Louis County, MO

No Signal is a message the monitor draws itself. It means the monitor has power and working electronics, and that the input it is set to carries nothing. Dell reads an amber or blinking power light on its monitors the same way, as power with no video coming in, and puts the problem in the computer or the cable. ASUS monitors use amber for the same state.

So the question that matters is how far the PC gets before a picture should appear.

A machine that never reaches its startup logo needs different work from one that shows the logo and then loses the picture as Windows loads, and a machine that was fine until you swapped memory or cleared the CMOS may need nothing but a few minutes of patience. This page follows that split. The free checks come first.

It is written for a PC whose fans spin and lights come on. If the power button does nothing at all, the PC is not starting, and that is a different fault, covered in computer won’t turn on. If the picture drops out for a second and comes back, the monitor keeps going black guide covers it.

Four checks at the desk

None of these needs a screwdriver.

1. Choose the input by name. Open the monitor’s menu with its button or joystick and pick the exact port the cable is in, HDMI 1, HDMI 2 or DisplayPort. Samsung notes that most monitors pick the live source on their own and sometimes pick the wrong one. It also warns that a monitor with two video cables attached may be listening on the wrong cable, so run this test with one cable.
2. Use the graphics card’s ports. A desktop with a graphics card has two sets of video ports on the back, and the card’s set is usually the lower one. Dell calls the motherboard’s port a common cause of a no-signal screen, especially on gaming desktops. LG gives the same instruction: with a dedicated card, the cable goes into the card.
3. Reseat the cable at both ends. LG’s version is to unplug it completely, look for bent pins or debris, plug it back in firmly, and try another cable if nothing changes. Take any dock, KVM switch or adapter out of the path while you test; Microsoft lists docks, dongles and adapters as a source of conflicts with external monitors.
4. Press Num Lock a few times and watch its light. This is LG’s test, and the answer splits the rest of this page. A light that turns on and off means the PC is running. LG reads a light that never changes as a PC that is likely frozen. On a machine that has just been switched on, I read it as a PC that never finished its startup checks. If the keyboard has no Num Lock light, use Caps Lock.

Some motherboard ports can never show a picture, whatever cable you use. Intel’s naming guide defines the F on a desktop processor as “Requires discrete graphics”, and AMD lists the Ryzen 7 5800X and the Ryzen 5 7500F as “Discrete Graphics Card Required” — on those chips the HDMI port on the motherboard carries nothing. Even with a processor that has graphics, Intel says some desktops switch them off once a graphics card is installed. Moving the cable to the motherboard is a test with a catch, then. A working PC can show No Signal there too.

Where the PC stops

Wait three minutes after new memory or a CMOS reset

A PC that has had its memory changed or its CMOS cleared retrains the memory on the next start, and the screen stays blank until that finishes. ASUS puts the training at about 1 to 3 minutes, depending on how much memory is installed, and asks you not to force the machine off while it runs. I treat the first boot of a new build the same way.

After training, a cold boot is far quicker. The ROG Strix B650-A I ran under a Ryzen 7 7800X3D took about 25 to 30 seconds to POST with a DDR5-6000 EXPO kit, as I noted in my review of that board. A screen still dark after a minute on an ordinary restart is worth chasing. After a memory change, a minute proves nothing.

I don’t read the debug lights, and I don’t touch the power button, until three minutes are up.

Read the debug LEDs

Many motherboards carry four small lights labelled CPU, DRAM, VGA and BOOT. ASUS calls them Q-LEDs and usually puts them near the 24-pin power connector or the memory slots, MSI calls them EZ Debug LEDs, and Gigabyte calls them Status LEDs. All three use them the same way. A light that stays on after power-up names the stage that failed, or in MSI’s words, the LED for the failing hardware “will remain constantly on”.

DRAM

ASUS’s order is to confirm each stick is fully seated, clean the contacts, use memory from the board’s support list, use the slots the manual recommends, and start on one stick before adding the others. If a single stick in the recommended slot still stops on DRAM, clear the CMOS as described below, then try other memory. ASUS’s last step for this light is to reinstall or change the CPU.

VGA

With a graphics card, ASUS says to reinstall it, clean the slot and the card’s gold contacts, and then try another card, and its graphics card guide adds a detail worth checking before any of that: on ASUS cards, a red LED at the power socket that stays lit points to the power cable, so reseat it and then try another. If the processor has graphics of its own, pull the card, connect the monitor to the motherboard and start the PC. MSI reads a picture there as a sign the card may have an issue. The Ryzen 7 7800X3D in my desktop allows this test, since AMD lists it with Radeon graphics.

The card-side work beyond that, from slots to power supply to BIOS settings, is in graphics card not detected.

CPU

MSI’s page covers two checks for this stage. One is the CPU power cable from the power supply. The other is the board’s CPU support list, because some boards need a BIOS update before they will run a newer processor. ASUS adds reseating the chip and checking the socket and pins for dirt or damage.

BOOT

Gigabyte’s manual says a lit BOOT LED means you haven’t entered the operating system yet, and ASUS points the same light at the boot drive. The board has already moved past its graphics light. With No Signal on the screen, I go back to the port, the cable and the input before I touch a drive.

No light stays on

Then the board believes it started. Press Num Lock again, and if the light responds, go to the Windows section below.

The minimal test and a CMOS reset

When the lights don’t settle it, or the board has none, strip the machine down. MSI’s test uses only the processor with its cooler, one stick of memory, the power supply and the monitor; USB devices, drives and other PCIe cards come out. If the PC shows a picture like that, put the parts back one at a time. The part that brings No Signal back is the fault.

Clearing the CMOS returns the BIOS to its defaults. MSI’s method is to disconnect the power completely, then either short the CMOS jumper, labelled JBAT1 on its boards, or remove the coin battery for 5 minutes. Expect the memory-training pause on the next start.

The logo shows, then Windows goes dark

If the maker’s logo or the BIOS screen appeared, the motherboard and the graphics card did their part. I treat that as Windows sending the picture to another display, or in a mode the monitor won’t accept.

1. Press Windows + Ctrl + Shift + B. Microsoft describes this as a reset of the graphics driver, and you hear a beep or see a flicker when it works.
2. Press Windows + P, then P again, then Enter. Microsoft’s blank-screen page gives that sequence for cycling the display modes, such as PC screen only, Duplicate and Extend, and you don’t need to see the screen to use it. It matters when a TV or a second monitor is plugged in and Windows is sending everything to that one. Repeat it a few times, a few seconds apart.
3. Unplug every display except one, and every USB device the PC doesn’t need to start. Dell recommends disconnecting nonessential devices when the screen is black at startup.
4. If the black screen began after a driver update, or after you raised the resolution or refresh rate, start in Safe Mode. Microsoft’s route is to hold the power button for 10 seconds to force the PC off, and to repeat that 2 to 3 times until Windows opens its recovery screen. Then choose Troubleshoot > Advanced Options > Startup Settings > Restart, and press F5 for Safe Mode with Networking.

In Safe Mode, open Device Manager, expand Display adapters, open the card’s Properties and use Roll Back Driver on the Driver tab. If the display mode was the trouble, set a resolution and refresh rate the monitor supports; ASUS’s monitor guide gives the same Safe Mode step. For a clean driver reinstall after that, the DDU steps are in the GPU driver crash guide.

DisplayPort no signal while HDMI works

A picture over HDMI and No Signal over DisplayPort means a working panel and a working graphics card. That leaves the DisplayPort link. BenQ’s list for this case covers these four steps, in the order I run them:

1. Open the monitor’s input list and confirm DisplayPort is there to select. If it is missing, BenQ’s advice is to check the cable is connected at both ends.
2. Unplug the DisplayPort cable and plug it back in, so the monitor detects the connection again.
3. If DisplayPort worked until recently, use HDMI to set the DisplayPort output to a resolution and refresh rate the monitor supports.
4. Update the graphics driver and the motherboard BIOS, over HDMI if DisplayPort shows nothing.

BenQ puts the driver and BIOS update before the resolution step. I leave the BIOS for last. I also suspect the cable here — if the trouble started when you raised the refresh rate or moved to a higher resolution, check that mode against the cable in the DisplayPort and HDMI bandwidth calculator before you buy another cable or blame the card.

A DisplayPort monitor that says No Signal only when it wakes from sleep has a separate fault, covered in the after-sleep section of the blackout guide.

When the monitor is the problem

The No Signal box shows the monitor can draw an image, so the suspect on the monitor side is its inputs. Connect a laptop or a console you know works, with the same cable and the same input. If that source gets No Signal too, try another cable with it. A monitor that shows nothing from two sources you trust has a fault in its input.

Before you call it, reset the monitor’s settings. On ASUS monitors the path is Menu > System Setup > Restore factory mode, and Dell monitors carry a self-test that checks the monitor on its own, with the steps for each model in its user guide.

Before you buy a part

Each branch ends at a swap. These are the points where I stop testing.

• The graphics card shows no picture in a second PC whose power supply meets the card’s requirement. That card is faulty; if it is under warranty, start the maker’s RMA.
• The DRAM light stays on with each stick alone in the slot the manual names, after a CMOS reset. ASUS’s next step is other memory.
• The CPU light stays on with the chip reseated, the pins clean and the CPU power cable connected. ASUS’s final step is another CPU.
• The minimal test still stops on memory and a processor that both work in another machine. What remains is the motherboard.