Question : Problem: My computer shuts down for no reason

My PC keeps shutting itself down for apparently no reason. It would shut down when I'm doing something, or when I just leave it alone. There's no countdown or warning in my case. The PC runs well for some time and then it just shuts itself down immediately, with no error screen, no warning or countdown. I turn it on and it shuts down in about 5 or 10 minutes. No warning, no nothing. Doesn't appear to be overheating and it doesn't "feel" like software. At times it will shut down but the computer will still be on.

System Information
   Operating System: Windows XP Professional (5.1, Build 2600) Service Pack 2            System Manufacturer: Dell Computer Corporation
       System Model: OptiPlex GX270              
          Processor: Intel(R) Pentium(R) 4 CPU 2.26GHz
             Memory: 254MB RAM

Answer : Problem: My computer shuts down for no reason

The Optiplex GX270s have a well known capacitor problem. Dell entended warranty period for affected motherboards. Your symptoms are consistent with failing capacitors.

Inspect capacitors on motherboard and see if any are bulging or leaking - pay special attention to ones around CPU socket. If any appear bulged, contact Dell and request a warranty replacement. I don't know if warranty extension has expired, but worth a try.