My HP desktop machine recently died. It is less than 2 years ol, and the only upgrade I have done is to replace the graphics card. My motherboard has no onboard graphics, so I must have a standalone video card installed in order to plug my monitor in. The card I had been running was a BFG nVidea GeForce 5500OC in AGP8x interface. My power supply unit is a Lite-On 250w, with 14a on the 12v rail. At the time it died, it had been running all night. The machine's case is not well-ventilated, and the room was pretty hot a lot of time. The following morning, I went to use the thing, and it was locked up. So I did a cold reboot, and got a black screen. The fans were all running, the hd was humming, but nothing...no boot, not even to the BIOS menu. After many hours of troubleshooting, testing the psu, the hard drive and all, I came to the video card. I removed it and placed a 64mb ATI card in one of the PCI slots, and voila! Success. So I am now buying and installing a new video card and a new psu to support it, and I am cutting vents in my case.