I've got a dual-monitor setup using a GeForce 7900GT that was working fine for over a year... then suddenly, only one of the screens works.

It's not OS-related, because even on startup, only one screen displays the BIOS checks. In the past, both screens would show it together.

• I didn't change anything to trigger this
• The monitor that gets a signal is random -- sometimes the one on the left goes black, sometimes the one on the right.
• The monitors and their cables are good -- I can switch both or either, and I get a signal just fine. They're plugged in, too.
• It's not the video card, either -- I have an identical 7900GT in another machine, and swapping the two didn't fix anything.
• It's not dust on the motherboard -- I pulled everything out, cleaned it off, checked for obvious damage, put it all back together, and no change.

My next two steps are going to be to reset the CMOS info and to try swapping out the motherboard.

Before I do that, does anyone have any other ideas?