If you are having problems with your keyboard or mouse, check the Logitech forums for help. If you think it is a hardware fault, try it on another PC to make sure it is the mouse/keyboard that is the problem (not your PC). If the problem is the same on the other PC, get the mouse/keyboard replaced.
Less than 30 days since purchase, you need to exchange it where you got it.
After 30 days, you would be covered under the 1, 3, or 5 year warranty from Logitech. See RMA info for replacement instructions.