Ok, this does not sound like it is software related anymore, but it is still possible. Here's what I would do:
-Check your motherboard's manual or website for a list of supported CPU's to make sure it is on the list. If not, this is why.
-Reset your CMOS. Sometimes settings in the BIOS can get wonky over time, and a good CMOS reset is what the motherboard needs. Look at your manual for how to do that properly.
-Some drivers may not be installed on your computer properly. This is quite an advanced part of the diagnosis. Do what I said first and then report back.