Computer Keeps Restarting on it's own what could be the problem?

So recently I had the fan and the heatsync replaced on my XPS 200 desktop because it was has loud as heck. After it was replaced (about a week ago) it worked fine. Yesterday I turned on the computer and in about 20 minutes after I started the machine the screen went blank and the computer just restarted. I do have anti-virus protection and a firewall (both are mcafee). So after I got something that read "Checking AT Bios". After that the dell logo came up and I got some other error but it went away withing 1 sec so i couild not read it. So I hit the power button and booted again. Now, when I normally boot my machine the fan will speed up for the first second or so then go quiet (thats normal). Now when I hit the power button the computer fan just starts like it normally does then it quiets down and then the computer restarts and does the same thing over and over. What could be the problem? Could it be something to do with the fan and heatsync that was replaced?

Computer Keeps Restarting on it's own what could be the problem?norton

i would guess its overheating or u have a virus ...

Computer Keeps Restarting on it's own what could be the problem?spyware remover

maybe that or a bad virus. better chack it out with a IT guy
viruses norton anti virus remove some programs some like virus protectors do it automatically or stop with the porn i heard that causes a lot of viruses.........