I do hope you did not crack the chip when fitting the heatsink,easy to do, you should get a beep at least on start up. No chip no beep! BIOS might not 'like' the new fan, its a long shot but i would replace the sink and fan with the old unit and try that. Good Luck Kitz E
Remove your processor, check all the pins are in place and undamaged reseat and attempt start up again if everything appears in order. If you have more than one memory chip try just running one chip on its own. Did you remove any protective film from the heatsink interface with the processor?