I suspect the CPU socket on this motherboard has gone.
So far as I have seen quoted, the s775 is only good for 20 insertions, the socket on this board appears iffy.
I have tried a quick exercise to get the pins straight but consider unlike prior to where I have been able to get a CPU working again, this time
around I have failed and do not want to lose a CPU for the sake of a bad short and the CPU being seated incorrectly.
Q - can you replace the socket 775?