So you overclocked your CPU too much on the motherboard and can't boot up?
Usually when your motherboard fails to post several time, it would revert the clocks back to default.
In the case it doesn't, is there a Clear CMOS button? If there isn't you need to use the jumpers to reset the memory on the motherboard, consult your manual. A quicker way would probably be taking out the battery for several seconds.