I have Win Xp installed in my Athlon 1800+. If i am not working on my pc, the pc will keep restarting by itself after 15, 30, 40 minutes... Any help would be appreciated.

Are you using an AGP graphics card? are you using a 300W + powersource? I went through similar problems with my sys, and upgraded just bout everything on my puter to no avail, finally i purchased a couple of programs that solved this problem. "Windows may stop responding when you use an Accelerated Graphics Port (AGP) program with an AMD Atholon processor. This is due to the memory allocated by the video adapter driver becoming corrupted." so I purchased a couple of programs from http://www.winguides.com the first two programs you see there "Tweak manager and Registry mechanic" may solve all your problems. They do offer a free 30 trial also. Give them a shot before you go dumping alot of money into upgrades. Oh and of course everyone will tell you to make sure you have all the latest drivers and updates on your system. good luck!

any luck with your system sarah?

So, far no luck. I tried few programs, but still the same problem.