Computer won't POST, stuck on VGA

[Gathering1802]

Yesterday my brothers PC just randomly black screened and become unresponsive. Upon restart the PC would no longer POST and the EZ Debug LED for VGA is on and there is no GPU output.

Specs:
Ryzen 5 2600X
MSI B450 TOMAHAWK
RTX 3070
Corsair RM750X PSU
4x8 GB of Corsair 3200 MT/s DDR4 RAM

I have tried the following:
- GPU in the other x16 slot and different GPU but still the same result.
- removed the CMOS battery to clear settings
- removed RAM sticks in pairs of 2

- measured the PSU with a cheap Chinese PSU tester which reports all rails are good (although it did report a PG of 80 ms - apparently a 'correct' PG would be 100+ ms). 

- reflashing the BIOS with Flashback.

- reseating the CPU in case the mount became bad (and immediately after pulling it out and remembering it's a PGA CPU remembered that's very unlikely) which also did not help.

 

By process of elimination this leads me to believe only the CPU or the motherboard could be at fault. I can try putting the CPU in my rig which has a 5600X to test the CPU but wanted to ask for any other ideas before I disassemble another PC.

Thanks for the suggestions

[strange13930]

have you tested the ram?

[Gathering1802]

5 minutes ago, strange13930 said:

have you tested the ram?

Yeah sorry, forgot to mention before I first took out 2 sticks, tested and failed, took out the other 2 stick and tested again (this time the RAM light lit up as expected), put back all 4 sticks only to be greeted by the VGA LED

[OddOod]

Best guess would be a dead motherboard, but can you put the GPU in a different tower and check that it's good?

[Gathering1802]

1 minute ago, OddOod said:

Best guess would be a dead motherboard, but can you put the GPU in a different tower and check that it's good?

The second GPU I put in the system to test is my old known to be good 1070. My guess is a dead MB as well, but I'm not sure how exactly it would fail to not boot a GPU on either the CPU or chipset PCIe slots...

[johnno124]

Given that you tried a different GPU with no success, i would think that either the motherboard had died or the PCIe controller had died. As @OddOod said above, if you have another PC to test the GPU on check. i fear it may be time to get a new motherboard though

[Sora1995]

I had this exact same problem. Surprisingly, the CPU was the problem, somehow. Replacing it got my system to boot again. Not sure why