I have a Gigabyte Z68X-UD7-B3 motherboard and it no longer recognizes both of my Nvidia GTX 580s. When I boot up it does not give me any errors and there is nothing obvious in the event log, but Windows can just only see one of them. Only one shows up in device manager, windows' resolution window or Nvidia's control panel. But here is the odd thing. Either card works alone in either slot, but if I have two cards in at once, only one of them shows up for Windows.
Just yesterday both cards were working at the same time. However, between then and when I noticed that only one was working now, three things happened. First, I accidentally broke off the end of one of the PCI slots by spacing on unlatching it before I pulled on it. Second, the bios failed to post and claiming that either I had changed the voltage or overclocked, it reset itself. Third, I upgraded the bios. So, to my mind, one of those things was the cause of my problem.
What I am trying to figure out now is if I need to replace the motherboard or if there is some bios setting or something that just needs to be updated. I know it sounds like a power problem, but it was running fine until yesterday and I have a 1200 W Thermaltake, which should be way more than I need. Could it be that somehow the power supply isn't working at full power after the broken pci slot or something? Or is there a setting in the bios about enabling multiple video cards somewhere? Or any other ideas? Or do I just need to replace the mobo? Given that I just snapped off the end of a pci slot just moving a video card, I'm kind of wary to trust myself swapping in a new motherboard, but if that's my only choice...
I tried reseting the bios to the optimized defaults, but that did not resolve the issue.
