Jumpy/jerky game?

[StellaInTheSky]

Sadly this is a whole different situation than lag (well, different than any I've experienced before, I've played around 2 1/2 years now). I actually defrag'ed my computer about 3 days ago after having this issue when I popped on for a while. No help whatsoever, game-wise. I keep nothing running in the background and if I open something I close it when I'm done. I've never thought of the computer restart before I play, I might have to test it out and see if it helps any. Thanks again!