I'm assuming its a wireless mouse, therefore as above sounds like the battery needs replacing. You might find a silly fix will be to take the USB Transmitter out, switch off the mouse, and remove the battery. Put the transmitter in another USB socket, replace the battery and switch the mouse on again. The P.C can sometime identifies a 'new device' and reinstalls the driver.

Otherwise I'm afraid its electronic...new mouse?

It sounds like it needs a new (or freshly charged) battery. I see similar behavior in my Logitech mice when the batteries get low.

Need more information... What things have you tried? Have your replace the battery?