First of all when did this problem start..did you do something or remember doing something, did u hear some sorta noise when u turned on the pc, did you remove the power cable and plug it in, does it have a power switch behind the computer where the power cable goes in. It could be power supply problem or something else you wont know for sure untill u show it to someone.

Where there is Fire...There is Coke. Where there is Rum..There is Smoke - Sir Smoke-a-Lot