[BaRRaKID]

From my experience in tech support most of the issues with mouses and keyboards are because of accumulated gunk, specially if you have pets or smoke near the computer. Since they are normally simple devices on the inside you can just remove the screws and clean all the dirt and you won't break anything. I actually just did this 5 minutes ago to my mouse because middle click wasn't working. Found out it was just a bunch of cat hair stuck in the mouse wheel. Other common source of issues is the USB cable, and those can be replaced if you know how to disconnect the contacts from the main board and resolder them.