My PC is fine whilst in BIOS. I have left in in bios for 10+ minutes, to check temps, and no problems there. As soon as I go into the OS(windows xp) however, it shuts down. PSU appears to be fine as far as I can tell, and mobo too(I started up without ram and heard the repeated, long beep). So I am pretty much stumped. It is a fairly old E-machine computer. Any other info you may need, in helping me to solve my problem, I'm more than happy to provide.