|Is it a mouse that has a ball underneath or a laser? If it's a ball, remove it and look inside the mouse for dust or dirt. If it's laser, you can't use a laser mouse on a reflective surface.|
If these don't work, try the mouse on another computer. If the problem persists, replace the mouse.
AMD Phenom II X2 550 @ 3.11
Patriot PC2-6400 4Gig
Seagate 160Gig SATA
Seagate 320Gig SATA