My Desktop Computer with XP shuts off automatically when not being used. It then starts up to the login screen. When I click on my name, it re-boots but everything I had been working with is lost.

All I can suggest is carefully check the control panel for an option to change or cancel the "time out" problem, I am having a similar prob. in Windows 7 !!

For win-7 click start button and type, require password when computer wakes, it may work in x-p ? it's been a while ?The other issue can be found not far from this one, in change when your computer sleeps, and disabling hibernation.