I'm having a similar problem myself. The scroll buttton on the mouse fails to zoom and, when clicked, fails to pan. It has happened to me before and after a few days of not using CAD, it started to function again. Now It doesn't work at all.This happens with new and existing files.
Note: I'm using 2010 ACAD and the mouse i'm using works in all other applications, this includes the scroll button.
PLEASE HELP! You don't realize how much you use that feature until it's taken from you. And your boss doesn't like excuses ha ha.