i recently bought a new laptop that came with windows vista, but vista sucks, so i downgraded to windows xp. when i installed windows xp, for some reason my notebook started to act weird. everytime i closed my lid, it would shut down and reboot, when it booted up, i would get some critical error windows saying something about windows has recovered from a serious problem.

so what i did was i went to power option
right click on your desktop > select properties > screensaver tab > click on Power button
then go to the Advanced tab and you will see a field called:
When I close the lid on my protable computer:

select Standy by (i had hibertnate)

so what all i did was to make it work, i changed it from hibernate to Stand by

then i did't have this problem anymore.