I've seen a lot of posts that seem to be about a similar problem, but nothing is exactly like the problem I'm having. My computer runs perfectly fine after I turn it on for anywhere from 5 min. to 3 hours, but eventually the monitor stops receiving signal and all audio goes silent. Also, the power button on the computer itself freezes at the same time the monitor goes out. I can hold the button down for minutes and nothing happens. The only way to turn off the computer is to unplug it. The computer seems to run fine except for the power button after the monitor goes out. All fans still run and everything sounds the same. The monitor works fine too. Also, no matter how many times it does this, it doesn't seem to get any worse. I tried changing the monitor connection from DVI to HDMI. Still had the problem. I tried hooking up two monitors at once (one DVI, one VGA), and both monitors stopped receiving signal at the same time. I tried cleaning the graphics card and doing some brief surface cleaning. Still had the problem. I tried rolling back the drivers on one of the graphics cards (which I updated about a month before I started having the problem). Didn't help. I tried doing a system restore as far back as I could (about 2 weeks). Didn't help. I tried waiting until the monitor went out, then switching the cable from the main graphics card to the back up card (both have an HDMI connection on back of the tower) without turning off the computer. The monitor stayed dark. I tried taking out the main graphics card completely, then booting with only the back up card. It seemed to last a little longer, but the monitor still stopped receiving signal. I tried leaving the computer off for 8+ hours, then trying again. Didn't help. I took out the main graphics card and put it back it. Didn't help. I've left the side panel of the tower off while the computer is running and everything doesn't get more than a couple of degrees warmer than the surrounding air temperature. Both my dad (who knows an awful lot about computers) and I are totally stumped. Unless both graphics cards are fried (and they both fried at the same time), it doesn't seem to be a graphics card issue. Both monitors I've tried are fine, and the computer seems to be fine, except for this. Help, please? If it helps, I'm running Windows Vista Home Edition. The computer is a little less than 2 years old. Both graphics cards are ATI Radeon HD, the main one is 4650, second is 3200 series (not sure of the exact number).