You maybe have vertical Sync off, the game can really, really lag if you have it off. In the corner of your screen i hope you got Nvidia controll panel ( its next to the time and it looks like an intellect buff green icon ).

Rightclick that, go to Nvidia Controll Panel, open that up, Look in the left for 3d settings, click under that tab for Manage 3D settings, scroll all the way down and the last one at my computer says Vertical Sync.
Click it and turn it off ^^

I hope it works,

Negativ1337