Originally Posted by skaven

Try going into a "manual" configuration mode and check that you've got the following settings:

FSB: 200Mhz
Multiplier: 11x (start turning this down if you still can't POST)
Mem FSB: 100%/200Mhz (this may be set to >100% by default for 166FSB procs)
CPU vCore: <default> (tick this up a bit if you're still having trouble POSTing)

Also, check your CPU temp. A poorly seated heatsink or absence of good thermal grease will cause the CPU to run too hot and thus not be able to POST at rated speed.