Could be a few things:
Drivers (try new one, or reinstall current version)
Background programs running and bogging machine down
Machine just needs a shutdown/restart
umm.. if you have tried another mouse then its probably not hardware. Being that its 'jerky' though, I would consider cleaning the gunk off the rollers inside the mouse.. 2 black ones and the white wheel.. on both mice to be sure..
After that.. no idea! Format, reinstall ;)
