some mainboards will not let you boot if the CPU fan sensor is not connected. you might check your new fan to see if the folks that made it put the wires in the terminal block(part that connects to mainboard) correctly. there have been several cases where a fan was not wired correctly to the block, just compare it to the old one. Another thing, check to make sure the CPU is fully seated, no need for high preassure,but it must be down completely.
Biostar T-force 4U,Opteron firstname.lastname@example.orgGhz.CorsairXMS DDR500-2gigs,EVGA7800GT CO.Seagate160gigSATA II,Koolance ICM 510 watercooling,Coolermaster Stacker830