Reset your BIOS - it might still be trying to use settings that were specific to your previous CPU....
Of course, if you have any specialized settings in there, make a note of them so you can change them back after the reset.
Also, check to see if there is a BIOS update for your motherboard ***that you need*** 0 as in it is made to work with Vista, or else it is made to work with your CPU family, etc.