Kay-
You've heard of "TMI"? Well, this is not "too much
information", could you provide more detail? What happens
when you turn the system on and what is your PC's profile?
-GH
Here are some possible causes:
1 - your computer has been stolen,
2 - you are experiencing a powercut
3 - your hands are tied bhind your back,
thus you cannot press the button on the computer