I assume you have cecked all BIOS settings, voltage, FSB, multiplier, etc. & checked more than a few times untill you are sure they should work, yes?
It sounds to me like your mobo is going with default values. There is usualy a setting somewhere in the mobo BIOS that you can switch on and off that will make the mobo re-set to default (Slow but safe) BIOS values to protect copmonents. If you set something drasticaly worng, it will either not be able to post withoit a "Clear CMOS" or it will go for default values.
If you are sure your BIOS is correct (At least mostly anyway) then ignore my post.
HAPPY PHENOM USER ! ! !!!