the number to call to get your mouse replaced for free if it comes to that is 1-800-360-7561. press 3, then1 to talk to someone to get your mouse replaced.
I hope you can figure out what the problem is, I have one of the old intellimouse (1500 scans) and it works just fun, even in all the onling gaming I do (RTCW, Q3, CS, DS, and WC3) peace
-spike