Gah mouse lag, can't bear it

[Octavian]

Every time I go forward a new page, I move the cursor and there's a bit of lag. It can't have something to do with my mouse, it must be something on the PC. Any suggestions?

EDIT - Yesterday it didn't say it needed defragging, now it says it does. The only thing I installed yesterday was the latest NVIDIA Forceware drivers. The other 20 or so gigs is made up of games.

EDIT 2 - Defrag is done, didn't seem to do anything. I'm getting lag in games, like CoD. Which I didn't before.