Have you tried taking the CPU back out and testing it in the other board? You want to move CPU's between systems as little as possible to reduce your risk of damage, but maybe you zapped it or somehow damaged it when moving or placing on the heatsink/fan. I would definately test the CPU in another system to rule this out.
If it does work in another system but on in your GA board, try resetting CMOS to clear the old settings. It is possible that the settings just are not kosher.