Basically age, would need more info, but sounds like Win 7 may be the newest thing there, the Core 2 Duos came out about 2006, you mention 4GB, if DDR3 would guess 1066 maybe 1333, and quite possible it DDR2...and good chance the DRAM is mismatched, many of those came w/ 1GB... A possible good thing is if it's a Core 2 8400, those cam at 3GHz stockl, but they OC well, could get a good cooler and should be able to take it up to around 4 GHz