Solved Post Failure: Video Card, Motherboard, or PSU?

Hello,

I was gaming yesterday when suddenly the computer just went black screen on me. I've built rigs for years and I'm stumped.

My current rig is built with:

CPU: i7 - 7700k
Motherboard - Gigabyte GA-Z270X-UD3
GPU-EVGA 3080RTX SC3 Ultra
M.2 NVMe - Samsung 970 EVO
SSD - PNY 250, Back up
RAM -16GB - T-Force Dark Gamer 2x 8GB
PSU - Corsair - CX750, 750W

Restarting the computer had all fans and led's turn on, but no post, no beeps, no display. The monitor did wake up, but blank screen, then went back to idle.
I reset the CMOS settings and got it to beep 5 times once, no post, no display. Thinking fried CPU.
Tried to restart it several times after, no beeps, no post, no display. Woke the monitor. The power LED's on the side connectors on the GPU remained off, thinking NOT the PSU... but who knows.

I proceeded to do a complete teardown, cleaning and reseating parts of the machine. CPU, RAM, Video Card, Connectors, etc and didn't see anything out of the ordinary. Put it back together, one stick of RAM at a time, and same result, no dice. Not likely RAM.

I pulled the side plugs to test the GPU power LED's, restarted and the no power/low power LED's came on, as they should. Still no start.
I removed the Video Card and tried using the internal GPU and it worked. Everything booted without issue. I tried putting in older GPU's, Nvidia 660, and 570 to test. Both gave me 5 beeps and failed to post as above. So I'm thinking, it's NOT the GPU's...

I wish I had some more left over parts to swap and test.

So I'm left with thinking its a fried PCI-e 1st, failing PSU 2nd, or all 3 video cards are bad, not likely??? Is that a sound conclusion? Am I missing anything?

I'm even writing this post on the machine, lol.

I'll try the second slot for the GPU and a CMOS one more time. I'll post after.

I'll be ordering a new, better PSU. That'll take a few days, but thoughts look right, yeah?

Same results on the second PCIe slot. It's never used.
I did notice more activity using the older GPU's . While the 3080 is completely silent, the 660 and 570 did not display but at least beeped 5 times.

I got my daughter to let me borrow a rig I'd built for her. The 3080 failed to post and had error beeps, very fast. Couldnt tell how many. The older cards booted, no problem. That rig also uses a 750W PSU.

I'm thinking the MB and 3080 both may have bitten the dust in this one event. 3080 has been RMA'd. If the board is toast, it might be time to upgrade.

Down time is annoying.

Here's hoping it's just the card.

Is it true that older GPUs may not be compatible with the newer MBs?

The RMA is away. Crossing fingers that is the case with my old cards and the current MB. If so, 5 beeps on a Gigabyte board may also mean incompatible GPU on top of CPU error. I will definitely post results.

Hi Rustys,
New card arrives sometime tomorrow. I will post results by end of tomorrow. Crossing fingers.

The card came in a day early ... and here I am. The problem WAS a dead Nvidia 3080 RTX. New GPU is running like a champ. The old 3080 RTX failed.

Take aways:
This computer used to work fine and suddenly had a "Black Out". The MB would not boot at all.
Seemed like it BRICKED until I pulled the GPU.
iGPU worked fine, but older GPUs would give a 5 beep error on POST without display.
Learned that GPUs older than a couple of generations might not work at all to test for a bad video card.
5 Beeps on boot up for a Gigabyte MB can also represent an incompatible video card. Not just failing CPU.

Thank you, Rustys for the tips you gave me. This is a very cool place to get computer information. I'll definitely be hanging around.