What is the beep sequence, how many beeps, lenghts? (1 long beep and then 2 short for expamle)
What BIOS do you have? You can usally see this when the computer starts.
DUST - Clear the dust from iside the case and off the fans. Compressed air is good for this. Turn of at the mains and disconnect everything.
Backup all of you work just to be on the safe side.