ive played Crysis on Very High and got a solid 25fps (with simpler bits at 30fps, and more complex at about 22) on my i7 PC, cause it is optimised for multiple cores. its just the program/game you are running isn't scripted to send its calculations to more than one core. majority of newer games all do, because the ps3 and 360 both at multi-core machines (360 has 3, ps3 has 8).

don't worry about it, there's nothing wrong with your PC, just slightly outdated programming.