What processor does it have now? WE can give you all kinds of proc.s that will fit the socket but, if you already have one of the best for the board/socket, you would be degrading your PC. It appears that it is a socket 775 from 2005. This leads me to believe the best CPU you could use/compatible would be something like a 3.4 GHz Pentium 4 HT with 800MHZ FSB; 3.40GHz 1M-Cache 800MHz FSB) [Prescott] OR , older Gen/lower clock [Northwood] units. Maybe, just maybe a Pentium D 820 would work (2M-Cache-2.80GHz-800MHz FSB) [Smithfield]