More information, please.
What is your primary boot device? CDROM? HDD? CF card?
Is the PC in your car? On your desk?
What sort of power supply is it using?
Really, man. This is like me asking for help because my engine is making a funny noise.
It reminds me of when I did phone support for Earthlink. Every call started with "I can't get my email". Never mind that some of these people had dead hard drives, a problem more serious than inability to access email. But that's the only symptom they see.
We can't help you without details, man.