Bad performance + mouse lag in games

I’ve never had any problems with performance issues on this computer. Recently I reinstalled windows and got a 22 inch widescreen, and since then all games I’ve tried have had mouselag and performance issues.

My specs are:
AMD Athlon 64 X2 dual core 4800+
2GB Ram
Nvidia GeForce 9800 GTX

I’ve been having trouble with all HL2 games(portal, TF2, etc) I tried Sims 3 out of frustration, and it actually had terrible performance. I can make things slightly better by setting down the graphics settings. But it doesn’t solve things.

In HL2, I had minimal to non mouselag if I had my resolution settings to a 4:3 aspect ratio. But as soon as I change it to 16:10 performance slows down and mouse lags appears.

I’ve tried reinstalling the drivers. Didn’t change anything. I’m guessing it has something to do with the widescreen and/or windows install. But I don’t have a clue on what to actually do.