MrNah

So I have this computer I'm fixing for a family friend that I thought would be easy. They didn't need any files so I just had to reformat there computer. They told me upon pick up that it restarts randomly. So during re-installing windows xp it restarted 2ce and it was always around the time I had to switch cd's (Its a MDG computer that has 2 cd's for the operating system). So then I started to think it was a hardware issue. So I tried a different hard drive, different ram and then after unpluging and replugging everything in I thought I'd try it again. It has a front door that covers the cd-rom and power button so I opened it, pressed the button and everything was working well. As Soon as I closed the door it restarted. Now every time I even shake it slightly it restarts. Any Ideas? What could it be? I've never ran into a case problem before... or could it be the power supply? Nothing looks outa the ordinary. Any suggestions would be awesome.

MrNah

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AMD Phenom 9850 Black Edition Quad Core Am2+ 2.5GHz 4M Cache
2x2GB PC6400 DDR2-800 Dual Channel x 2 = 8GB Ram
Asus M3A AMD 770/SB600 AM2
Seagate 500GB 7200RPM 32MB Buffer
EVGA e-GeForce 8600GT 512MB DDR3 PCI-E
Coolmaster Setup - Windows Vista