If you've just bought your computer less than a year or two and you're new to the realm of computers/internet, you might just want to do yourself a favour by checking the rollers next to your mouse ball, they are 90 degrees perpendicular to each other. Reason is the dead skin gets collected there until it was half a centimeter thick! When I scraped the 'thing' out, it was like one long wafer of dead skin and it was GROSS! I would recommend periodic cleaning of your mouse to prevent such unpleasantries from coming up unexpectedly.
Jag
P.S. Not applicable to users of Optical Mice.
Jag
P.S. Not applicable to users of Optical Mice.