Need some ideas - intermittent GPU detection / boot device failure


Posts: 285   +2
Ive come across a problem I cant solve myself this time round.

PC is I5 4690k, Z97A motherboard, 8gb ripjaw ram (2133?) corsair tx750w PSU, evo 840 SSD
CPU has been overclocked for probably 3 out of 6 years, but isnt anymore.

Was using this PC only a few weeks ago. recently got 5800x, so moved the 980ti to new system with that, used for a few weeks, then replaced with a rx 6800. Rebuilt the old system to give to a friend but im now getting seemingly random VGA red lights and boot device red lights, sometimes together.

What have I done:
Cleaned everything
reseated GPU no end of times
Fresh win 10 reset
reinstalled GPU drivers
updated motherboard BIOS
Reseated all connectors

GPU and CPU seem fine, and will game no problem, run furmark and prime95 no problem its very strange.
At first I thought it was because I used an 8+6 off 1 rail, swapped it to power from 2 rails, no difference
Then I thought it was the GPU not seated properly, as CPU power cable was running underneath GPU. addressed but no difference
Then I thought it was the CMOS battery being dead, swapped for a known good one, no difference.

I did a table of 5 shutdown/powerups and 5 restart powerups with the case both in a vertical and horizontal position (because I still think GPU seating could be a factor), here are the results:

Horizontal: Vertical
Shutdown/powerups Shutdown/powerups
1 - success 1 - Success
2 - success 2- success
3 - VGA & Boot Device light - failure 3 - success
4 - VGA light, CPU fan stalled - failure 4 - VGA & Boot Device light - failure
5 - VGA light, CPU fan stalled - failure 5 - success, but few seconds slower to boot

Restart/powerups Restart/powerups
1 - Success 1 - success
2 - Success 2- VGA & Boot Device light - failure
3 - Win recovery screen, no leds - failure 3 - VGA light - failure
4 - VGA & Boot Device light - failure 4 - success
5 - Success 5 - success

Not sure what to make of that data. I think the win recovery was probably due to all the restarts. My thought is a motherboard or ground issue, as if it was cpu or gpu issue, id be seeing other symptoms like black/bue screens, crashes etc.
Im going to do a stripped purely POST test outside the case next week, but in the meantime...

Any ideas?
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