PC mice are usually used by older computers, they have a ball at the base of the mouse that rotates as the mouse moves. As the ball rotates, it drives a set of optical encoders that measure the distance and direction that the mouse has moved. The mouse then sends this information to the host computer, which moves the mouse pointer on the screen. One problem with mechanical mice is that the ball can pull dust and dirt into the mechanism; this can stop the ball from rotating smoothly. If this occurs, remove the ball and clean the rollers.
Turn the mouse upside-down to reveal the ball. Twist the cover around the ball in the direction of the arrows, then lift it off.
Turn the mouse over, holding your palm underneath to catch the ball as it drops out. Wipe the ball with the damp cloth, then dry it with the paper towel.
Remove any built-up dirt on the rollers with the cotton swab. There are two rollers inside the mouse -- one to measure the up-and-down motion, and the other to measure left and right. Scrape away any stubborn dirt using a flat-head screwdriver. Clean both rollers until they are completely free of dirt.
Turn the mouse upside-down and drop the ball gently back into the mouse. Replace the cover and rotate it to lock it into place.