Does it only have the problem in the car? Is so, it's prolly a power issue. Recalculate your power usage and give a little room to be sure. If not.....
Try boot from CD?
If that doesn't work then.....
Try removing everything cept memory, video, hdd. Then try to boot. If it works then add back other components 1 at a time. If it doesn't boot remove the hard drive and see if it'll tell you it can't find an OS.
If it still doesn't work try removing your memory one at a time if there are two modules. If not try to swap it with another one.
Then you could always try resetting the BIOS. I've seen BIOS' hit by a stray static charge that screwed them up and a reset fixed the issue. *shrugs*
Or you could do what a friend of mine did. ***** and moan about the computer cuz it ain't working. Go buy a new one and give me the old one only to ***** and moan that I got it working perfectly with only a new hdd. Then ***** and moan some more cuz I wouldn't give it back
