the first rule of thumb is always to see if it is virus/malware related. So run those first. If they come up clear, then it could be other issues such as driver issues, drive update issues and such.

Is your mouse connected remotely (via USB stick) and uses batteries?

Or is it hooked up to your tower directly(via a line) and has a purple looking connector (we call those scuddsy connections)

if it is done via a line and doesn't use batteries, then it might not be the mouse itself at all but other issues such as its own applications.

You can try to reload your driver by inserting your original cd that came with your computer, it should say "drivers and applications" and let it run, look to where it says "mouse and pointing devices" and then try to reintall the driver that way.

but before that, I'd try to update your driver first (if that IS the case)
you can do that by going to your "Start" scroll to "My computer" and right click. scroll down to "manage"

find "device manager" and double click on it (left click)

find, "mice and other pointing devices"

double click on that. Your mouse info should be there. If it tells you the device is working properly, you can leave it alone or click on "troubleshoot" and try that.

If that still doesn't solve your problem, at the same window, click on the "driver" tab. And select update drivers. This is where you'll need your drivers and applications CD. (this is what Bobbie suggested I just added more details. LOL)

But I would try other things first before you do that.

Also, when was the last time you cleaned your cache, defragged, and cleaned out your system?

and are you using your original "arrow" pointing cursor or have you downloaded one of those pretty cursors designed by someone else. If so, uninstall those.