I agree with the others that the processor is likely not supported by the computer, but there are a few things to try:
Reset the BIOS, see if that helps
Check for a BIOS/Firmware update on the manufacturer's website, they may have added compatibility.
Once when adding an aftermarket cooler I got some thermal paste on the under side of the CPU which prevented POST. thankfully nothing was damaged, I just had to clean it off and it started working again.
If none of that works then I am afraid you are up a creek. Everyone complains that Intel changes their pinouts too often, but this is one case where the platform lasted too long, and it causes far more confusion than it is worth.