You press the power button, the fans spin, the lights come on, maybe the RGB lighting starts up, but the monitor stays black or says “no signal”. This is called a “no POST” fault: the PC is getting power but not finishing its power-on self-test, the checks it runs before showing anything on screen. The good news is that most desktop motherboards will tell you where they got stuck, if you know where to look.
Rule out the simple things first
It sounds obvious, but a surprising number of “dead” PCs turn out to be a display problem:
- Check the monitor input. Make sure the monitor is set to the right input (HDMI 1, DisplayPort and so on) and try a different cable.
- Use the graphics card’s outputs. If you have a dedicated graphics card, the monitor cable must go into the card, not into the ports on the motherboard’s back panel. Those ports only work with a processor that has built-in graphics, and only when no card is fitted or the BIOS is set up for it.
- Try another screen. A TV with HDMI is a quick test.
- Wait a little longer. After a BIOS update, a CMOS reset or new memory, many modern systems spend a minute or more “training” the memory before anything appears. Give it a couple of minutes before deciding it has failed.
Read the motherboard’s debug LEDs
Most motherboards from the last few years have four small LEDs near the memory slots or the 24-pin power connector, labelled CPU, DRAM, VGA and BOOT. During startup, each lights briefly as the board checks that part. If the PC stops, the LED that stays lit shows where:
- CPU: the processor isn’t being detected or initialised. Causes include a BIOS that doesn’t support that processor yet, a loose 8-pin CPU power cable at the top of the board, bent socket pins or a failed processor.
- DRAM: the memory check failed. This is the most common one. It can be a stick that isn’t fully seated, the wrong slots, incompatible or failing memory, or an unstable XMP/EXPO memory profile.
- VGA: no working graphics was found. Check the graphics card’s power cables, reseat the card, and try another card or the onboard graphics if your processor has them.
- BOOT: the hardware checks passed, but there is no bootable drive. That usually means a storage or boot order problem, not a display fault.
Higher-end boards often have a two-digit Q-code display instead of, or as well as, the LEDs. The codes mean different things on different brands, so look up the exact code in your motherboard’s manual rather than a generic list.
Some older or budget boards have neither, but may beep through a small speaker if one is fitted. The beep pattern can be looked up in the manual too.
Safe checks you can do yourself
Switch off at the wall and unplug the power cable before touching anything inside. Touch a bare metal part of the case to discharge static before handling parts.
Reseat the memory
Take the memory sticks out and push them back in firmly until both clips click. Then try a single stick in the slot your manual recommends for one module (often the second slot from the processor). If the PC starts with one stick but not another, you have found a faulty module or slot.
Check the power cables
Make sure the 24-pin motherboard cable, the 4+4 or 8-pin CPU cable(s) at the top-left of the board, and every power connector on the graphics card are fully pushed in. Recent high-power graphics cards are fussy about properly seated connectors. If a connector or socket looks melted or discoloured, stop and get it checked.
Clear the CMOS
Resetting the BIOS settings undoes an unstable overclock or memory profile. Your manual will show how: usually a button on the back panel, a jumper, or removing the coin-cell battery for a few minutes with the power disconnected. Expect a long first start afterwards while the memory retrains.
Strip it to the minimum
If you’re still stuck, disconnect everything that isn’t essential: extra drives, USB devices, front-panel accessories and any expansion cards other than graphics. Run with one memory stick and the graphics card only. If it starts, add parts back one at a time.
When it needs a technician
Stop and get help if:
- the same LED stays lit after you have reseated, reset and minimised everything;
- you smell burning, see scorch marks, or the PC switches off within a second or two of pressing the button;
- the problem started after a power cut, a liquid spill or moving the PC;
- you would need to remove the processor cooler or processor to go further.
At that stage the cause could be the power supply, the motherboard, the processor or the graphics card, and the reliable way to find out is to test with known-good parts. Buying parts one at a time on guesswork can easily cost more than a diagnosis.
If the PC has files you can’t afford to lose, remember that a no-POST fault almost never damages the drives. The data is usually still there and can be copied off once the fault is found, or recovered directly from the drive.
Book a diagnosis
We build and repair desktop and gaming PCs, and test with spare known-good parts to find no-display faults quickly. If you’re worried about the files on it, our data recovery service can get them off safely. Call Creative IT on 020 7237 4908, bring the PC to our Central London repair centre, or use our UK-wide courier collection. Evaluation is free, you get a fixed quote before any work, and there is no fee if we can’t fix it.