cybersitter support

Help! My computer is messed up!?
ATTENTION!: My computer is messed. This started very recently. It used to work perfectly fine until now. Every time I turn it on, it’ll start and then a couple of minutes later, it’ll randomly shut off. I have no idea why it does this. I’ve run many virus scans with the protection programs, (Zone-Alarm, Cybersitter, CA etc.) but all of them say that the computer is fine. I looked for anything quarantined but there isn’t anything like that. (BTW I have Windows XP with all the updates!). I called tech-support but they can’t figure it out, and neither can the Windows Computer company people. I can’t even msn :’( I tried buying a new motherboard. I don’t know if I should buy Windows Vista or not. If you know whats wrong with my computer and/or how to fix it, please tell me! Thanx!
did u try updating your version of XP to service pack 3? they fixed a bug like this in there, hope this works.
also the vista motherboard is a bad idea because your other hardware might not work well with that motherboard, call your computer manufacturer and ask if that board will work.