My friend has recently moved houses. Before he moved, his computer was perfectly fine. Specs:
ASUS P5Q PRO
Some "excool" 500 watt PSU (it has been working fine for 3 years+)
2 + 1 gb ddr2 800 mhz ram
500 gb 7200 rpm hard drive
Windows XP Home Premium SP3 32 bit
Now ever since he has moved hosue, his screen has been black-screening. He has only had the PC in his new house for a day or two. He was playing BFBC2 for about 20 minutes and then it suddenly balck screened. He couldn't find his DVI cable so he used a VGA cable to play. 20 minutes in, the computer black screened. Thinking that the cable was faulty, he found the DVI cable the next day and used it. Now it won't even POST. Fans will spin up for 5 seconds and then power down. He suspects that the power point or power supply is causing these black screens.
Nothing is overclocked, all temps are good (max it has been is 45*c).
Maybe something shifted in the case when it was moved or it was banged on something. I had this happen a few times and usually its a ram stick or maybe your video card moved 'O so slightly but not enough to notice. If you know what you are doing, then remove and put the ram back and see if that helps. If not then try the video card. Check the cables and see if everything is fine. This is a normal thing and I find this happens quit often being a computer repair man. I fix many computers that I only spend 2 minutes on and which is awesome as its easy money.