why does no games run good on phenoms? (jumps off a cliff) P.S I have two 4830s crossfired so graphics isn't the bottolneck

Help? my computer can only do 24fps in this game with all the setting put on high at 1440 by 900 I have a AMD phenom 2.2ghz quad, ATI 3870 512, 4GB and win vista ultimate, what do I do to get the frame rates up?