Possible video card failure

I tried to make a topic once, but for some reason it's not showing up. My apologies if this is spam.

Anyways, I just recently build a new gaming computer. It's the first time I've built one, so I'm kinda new to hardware troubleshooting. The video cards in question are 2 Sapphire HD4850's 512mb HDMI in crossfire mode.

Basically, everything has been working great for the first two weeks, then today while playing a game I got this buzzing noise accompanied by loss of video. Thinking back I'm not sure if I can specifically define it as a crash or simply a loss of video. My memory is already getting fuzzy. Anyways, I restarted the computer, which came on just fine except for no video. No beeps, no strange noises, just a black screen (monitor remained in standby mode). I then restarted again, except this time with the DVI cable plugged into the secondary card instead of the primary. Video was restored, but when I brought up the CCC, it only showed 1 of the cards. I looked inside the case and saw that both gpu fans were running at normal speed, and when I shutdown the computer both red power LED's flashed appropriately.

At no point were there any error messages or, as far as I can tell, any indication that there was a problem.

Is there anything I should check before I assume it's a hardware failure? I submitted a ticket with Sapphire already, so we'll see what they say, but if there's anything I can or should do first, I'd appreciate the advice.