Okay, we got a start there but a little more info will help. Is it not doing anything from the restart option in the start menu (trying to exit windows)?
Or is it that it just does not power on when you push the button?
it could be your anti virus or a damaged file. try two things..one boot into safe mode using f8 and see if the error still there. if it not then it a program that loaded that hanging the system. to find out which one use msconfig and under the start up tab turn all the programs off in start up and reboot. then go back and turn one program on at a time till the error comes back.