If I wait about 20 minutes, then it will turn back on.
This is a clue that it is a heat related issue. It is possible that your processor is overheating. Clean the fan and cooling fins on the processor cooler, and all the other fans while you are at it. Another symptom of the processor overheating is that often the computer will run really slow right before it shuts down.
It is also possible that you have a failing power supply. Again, heat related, but failing none the less.
Do you get a blue screen flash when the computer shuts down? Usually when XP automatically reboots it is because Windows recieved an error. We need to make a change to a setting on your computer so we can find out exactly what the error is.
Go to:Start > right click My Computer > Properties > Advanced > Startup and Recovery Settings
and uncheck Automatically Restart
. Now when Windows receives an error it will show you a blue screen.
Blue screens are often called 'Blue Screens of Death' (or BSOD) by users, and 'Stop Messages' by Microsoft. We need to know the exact message you see when you get the blue screen. We especially are looking for a set of letters and numbers about half way down the page that take this format:
This is usually followed by a set of 4 simliar numbers in parenthasis. For now we just need the first set of letter and numbers (before the numbers in the parenthasis).
This will help you diagnose why you are getting the stop messages, if in fact you are getting them. If you computer is simply overheating, then you probably won't see the blue screen.
Let us know if any of this makes sense. I mean, you are the one that can look inside your computer to see if the fans are running and if they are clean, etc.