After loosing half an hour of my life to a dirty chip.. i have discovered 2 things :
the l33t art of on-chip moddin!
that when a cpu doesn't work , CLEAN it with rubbing alcahol/acetone , reapply the paste and then pop it back in .
My AS5 was all over one of the ICs because i had removed the heatsink , the CPU would boot up @ 600mhz, 100 FSB , attempts to overclock it would result in a no-boot . It is known that connect the little metal thingies on your CPU with a conductive line [ graphite pencil] can force the multipiers/bus to change . Apparently AS5 conducts electricity just fine, and it forced my cpu to 600mhz .
When your CPU refuses to work, [and you recently played around with it ]
clean your chip, the try it again!