Uhh, not all CPUs are compatiable with all motherboards.
Infact they're extremely limited.
The mother and CPU socket both have to match. I.E. LGA 775, LGA 1155, LGA 115, AM3, FM2, ect.
And sometimes even if the sockets match, the motherboard doesn't support the CPU either because it needs a BIOS update or the manufacturer has discontinued support for the board but new CPUs still came out, or CPUs with a higher power requirement than what the motherboard can deliver.