Windows shuts itself down

[Jrwhite8]

I have a custom built computer with Windows XP that I've had for about three years. The last month or so it has been acting up. When I turn on the computer, then click my name to log in to my account it does so without a problem. But then whenever I click a program, either immediately or after a few minutes the computer all of a sudden logs me off and shuts itself down. It doesn't just turn off, leading me to believe it's a Windows problem, not a hardware problem. And here's the funny part: if I log in to my account, then quickly switch users and log into another account, when it tries to shut down a message pops up saying "Other people are logged on to this computer. Shutting down Windows might cause them to lose data. Do you want to continue shutting down?" And if I just ignore that window, I can stay on the computer as long as I want. It seems like if I can "trick" the computer into not shutting down, the problem isn't that serious. Any ideas how to fix it?

 

[IronDuke]

The easiest option would probably be to create a new user and then delete the current one.

 

[Jrwhite8]

It doesn't matter which user name

It doesn't matter which user name I'm on, they all shut down. It's only if I'm on any 2 user names at the same time that I can trick it into not shutting down.