GTX 970 won't POST---power supply or motherboard?

[Ftracy3]

This is headache I'm trying to narrow down to the card, the motherboard, or the power supply. I have an intel DP67BG motherboard that has worked fine with two raedon 6790's in crossfire for a few years. I upgraded the video to a GTX 970..at first after installing the card the machine wouldn't post..the cards, fan would spin, but it would hang in the POST LED sequence on the motherboard at the CPU (right before video detection), and restart, Eventually it worked after installing the old cards, reinstalling the new one, etc. Now four months later one day the sound stopped working, the computer hung and again when it rebooted it would go through an endless attempt to Post, shut down, restart cycle. Installing the old boards worked--although there was some intial trouble detecting them as well this time around (I think they weren't seated properly).
So my question is about the power supply, which is a cheap 500 watt one that came with the build. Is it possible that a problem with the supply would allow one card(s) to POST and another not to? The GTX 970 actually draws less idle power than the AMD cards so this wouldn't make sense to me, unless the GTX might be more sensitive to power variances. Other than this I've seen no indication of power problems--no crashes under stress or anything. So if it's not the card, what would be the more likely culprit if one card not working and the crossfire pair working fine?

 

[Dark Lord of Tech]

Did you uninstall the old GPU drivers.

 

[clutchc]

There's also a slight chance that the MB BIOS doesn't recognize the newer Maxwell-equipped GPU with its UEFI BIOS. If your old card works, that would be my thought. The GTX 970 is only a 145W card. And as long as you have the 6 pin fed, 500W should be OK for boot and idle power.

 

[Ninja Removal Expert]

He's not getting far enough to un-install the drivers. His PC wont even start with the 970. There are 2 possibilities that I can think of... you have a broken 970 card - put it into another PC to test this out. Or somehow your board is incompatible with your card. Look on the manufacturer forums about incompatibilities that other people may have reported. using the old cards look in your BIOS for settings that might prevent the 970 from working. Is crossfire enabled or forced in the BIOS? Are the PCI ports in some kind of custom setting, like speed set manually... try changing it or setting to auto if such a setting exists. Also try booting to windows and flashing your motherboard BIOS to the latest manufacturer version.

 

[Karadjgne]

Ppl have shown incompatibilities with Maxwell gpus and older, non-uefi bios. That can be an issue.

Uninstall in old gpu drivers is easy. Insert 1 of the older cards, boot, uninstall drivers. Any gpu will work with standard vga default drivers. A driver cleaner utility usually works best. Then reinstall new card.. Yada Yada Yada.

A cheap 500w is pushing the luck. Most don't have enough on the 12v rail, and end up shotrtchanging the gpu. More than 1 supposed 500w unit should really be classed in the 300-400w range.

My best guess is incompatible bios.

 

[Dark Lord of Tech]

What windows are you running?

 

[Ftracy3]

Running Windows 8.1..but the card worked for a few months. I would say it's card failure except for the fact that it exhibited this same behavior when I first installed it...installing and uninstalling old cards solved the problem. I have uninstalled all AMD drivers using install manager and Driver Fusion (using old card) before installing new Nvidia one. Anyway I've RMA'd the card but am trying to figure out what else could cause this problem. I guess the question I was wondering is if the power supply is sending variable and outside of norm power fluctuations, would one card (actually a two card crossfire) be able to handle it better than the other? I don't want to go buy a new PSU to test this theory if it's not even likely. I don't think it's the MB bios or the card wouldn't have worked for a few months.