Weird Left 4 Dead frame-rate issues

[ryujians]

I just bought left 4 dead because there was a good deal on it in steam but i am experiencing a great amount of lag even in single player. There is no lag moving forward in game but when i turn side to side it lags pretty hard. 

 

My specs should be plenty to play this game

-FX 8320 stock

-HIS hd 6850 1gb

-2x4gb ram

-1tb hdd

-1440x900 monitor, i'm upgrading after i get a new gpu will be a while though

- MSI 970a G46 i recently replaced the mobo so is there something i need to do to get it formatted better, i don't want to loose all my downloads either.