look here
http://support.microsoft.com/default...b;EN-US;310117
this is an article telling about the OPPOSITE problem from what you have
it is telling how to STOP the computer from auto shutting down ....so check it out and do the OPPOSITE from what it says, lol
Click Start, click Control Panel, and then double-click Power Options.
Click on the APM tab.
Uncheck the Enable Advanced Power Management Support box.
so probably you would make sure the apm box is CHECKED