PC suddenly stopped displaying — GPU works in neither PC, CPU/VGA debug lights confusing me

[u/Any_Hawk_235]

​

Hi! I've had some problems with my PC recently and I'm completely stumped as to what the problem is.

My PC originally stopped displaying after I had left it running. When I came back, the computer itself was still on, but there was no display. I turned the monitor on and got nothing.

I initially suspected the GPU, so I tried different HDMI cables and other basic troubleshooting. I then put my husband's known-working graphics card into my PC, but I still got no display.

I then started testing the RAM. I have 4 × 8 GB Corsair DDR4 RAM. I tried running the PC with two sticks and then with just one. I noticed some very strange behaviour: with two sticks installed, my keyboard and mouse wouldn't light up, whereas with four sticks they would.

There was also one occasion during troubleshooting where the display briefly came back and the PC successfully booted into Windows. It stayed working for around 4–5 minutes, and then the display cut out completely again.

I have also tried clearing the CMOS. After doing this, I briefly got a message on the screen saying that the CMOS had been cleared. This was while using my husband's graphics card. However, that message never appeared again, and I haven't been able to get any display since.

The GPU testing is where I'm especially confused:

- My husband's known-working GPU in my PC: no display, and the CPU debug light comes on. There is no VGA debug light.

- My RTX 3060 in my husband's PC: no display, and his motherboard shows a VGA debug light.

- So both PCs are giving different diagnostic lights depending on which GPU is installed.

My current specs are:

- CPU: AMD Ryzen 7 5700X

- Motherboard: MSI B550-A Pro

- GPU: NVIDIA RTX 3060

- RAM: Corsair 4 × 8 GB DDR4

- PSU: Corsair RM650e 650W

I have already replaced the PSU because I've had power surges in the past and initially assumed the PSU had failed. I completely rebuilt the PC today, but the problem is still there.

So I'm really confused about what is actually faulty.

The symptoms seem to point in different directions:

- My RTX 3060 doesn't display in my PC.

- My RTX 3060 also doesn't display when tested in my husband's PC, where it causes a VGA debug light.

- My husband's known-working GPU doesn't display in my PC, but my PC shows a CPU debug light instead.

- RAM configuration seems to change the behaviour of my PC.

- I have successfully reached Windows once, but only for around 4–5 minutes before losing display again.

- I have successfully received the CMOS-cleared message once, but haven't been able to reproduce it.

- The PSU has already been replaced.

- The PC has been completely rebuilt.

At this point, I'm wondering whether I could have a problem with the GPU, motherboard, CPU, RAM, or potentially multiple components.

All of my tech-support friends are completely stumped too. I don't mind buying replacement parts, but I really don't want to start replacing perfectly good components at random.

What would you test next, and is there a way to determine which component is actually faulty before I start buying new parts?

I can provide photos of the motherboard/debug LEDs and any other information that would help.

[u/Fresh_Inside_6982]

Bad MB most likely, could be CPU, swap out parts until you find the bad one; no magic way to diagnose.

[u/Any_Hawk_235 → u/Fresh_Inside_6982]

MB is my prime suspect. Just strange that my GPU is not working in my husbands computer. Unless my mobo and gpu decided to die together, if my luck is very very bad.

[u/Most_Cicada3939]

have you cleared the cmos when changing gpu's?

[u/Any_Hawk_235 → u/Most_Cicada3939]

Tried before removing mine and again before installing the known working 4080.

No change when I did this with my GPU in.

When I cleared it and tested the 4080, I briefly got the cmos cleared message. Haven't been able to get one since though. No integrated graphics on my cpu so.

[u/Most_Cicada3939]

power supply cable to your card same used for both gpus? could be original gpu and cable to gpu that got burnt?

[u/Any_Hawk_235 → u/Most_Cicada3939]

Replaced PSU today, all new cables! 🥲

[u/Tech_surgeon → u/Any_Hawk_235]

still sounds like power getting cut off some where so i wouldn't be shocked if the cpu or mother board has a broken circuit path on it that comes back to life at random.

[u/Any_Hawk_235 → u/Tech_surgeon]

I'm 99% certain it's not the cpu but as I research I'm hearing all sorts of shit about MSI mobos. 10 months old. If it's broken I'd be pretty miffed.