Hi
Most modern socket 775 motherboards support most core 2 duo or quad CPUs
Older ones may need a bios update or not support latter core 2
What motherboard do you have , there will be a supported cpu and ram page on makers website ( often with bios levels required)
Installing or using a older cpu while running bios update may be only way round problem
Getting correct bios is critical especially if there is no dual bios
Regards
Mike Barnes