This is a long tale, however, my computer kept restarting after i'd logged in, so thinking it must be a virus, i had to take the hard drive out of the machine and put it in an enclosure and run it through two different virus checkers, spybot and malware bytes attached to another computer. the hard drive seemed to be clean then, so i hooked it back up to the computer, but the computer then wouldn't even get to the login screen before it would restart. i tested the ram, it was good. i backed up the hard drive, reformatted and am now trying to re-install windows xp. the problem is, is the computer starts going into the windows install, then suddenly restarts again. I've tried resetting the bios/cmos, i've tried booting from an external cd rom. i've disconnected the internal cd rom and floppy, and am trying the reinstall from an external usb cd rom, but the computer keeps restarting before the windows re-install will finish. It just now started making this siren sound. The fan is turning on the mother board and at the back of the machine, but the siren keeps going. I'm out of thoughts on this. Any help would be appreciated.