Most modern mice come equipped with a "scroll wheel," located in the center of the mouse, between the left and right buttons. As the name indicates, it allows the user to scroll horizontally--or, in some cases, vertically as well. This is helpful when viewing websites or documents that fill more than the entire window.
But if dirt or debris get trapped inside the wheel, or if certain drivers or settings are in place, the mouse wheel may malfunction, rendering it unusable. Usually, repairing a scroll wheel is relatively easy.
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Unplug the mouse from the computer. Flip the mouse over so that the bottom is facing up. Unscrew the bottom cover. The location of the screws will depend on the mouse.
Use your forefinger and thumb to lift the scroll wheel from its tray. Depending on the model, you may need to lift the entire circuit board and squeeze the latches located on the bottom of the board to release the scroll wheel.
Remove any debris you find trapped in the tray. If the mouse wheel is at all dusty or sticky, use a soft, damp, antistatic cloth to gently wipe around the circumference of the wheel. Do not tug at or pull on any parts attached to the mouse wheel.
Place the scroll wheel (and the circuit board, if necessary) back into the mouse. Screw the bottom cover back into place. Plug the mouse back into the computer. Restart or power on your computer.
Check your scroll wheel. If it's still not working, go to "Start," then "Control Panel." Double-click "Mouse." Check your mouse's settings to make sure the scroll wheel option has not been disabled.
Return to "Control Panel." Double-click "Device Manager." If you are using Windows Vista, click "Approve" when the "User Account Control" dialogue box appears.
Click the plus sign next to "Mice." Right-click your mouse from the list. Click "Update Driver Software."
Click "Search automatically for updated driver software." If a new driver is found, follow the on-screen instructions to install the new driver.