Have you tried the obvious of Clearing the CMOS settings?
Turn off the PC and unplug the power cord
Move the CLR_CMOS jumper cap from pins 1-2 (normal) to pins 2-3 (clear CMOS).
If that doesn't make it work then you will need to remove the MOBO completely from the case and inspect it for visible damage.
Sometimes the combination of replacing the standoffs then remounting the MOBO after reseating the CPU with fresh thermal paste (when MOBO is flat on wooden table or similar, outside of case) does indeed fix certain boot issues.