I used to have a mouse that did exactly the same thing. If I switched off the computer, jiggled the mouse connection a bit (hope that language is not too technical for you!) and then switched on again, it worked. I reckon you've got either a dodgy connection in your mouse somewhere or a dodgy usb port. As already suggested by someone else, try plugging it into a different port and see if the problem recurs. If it does, I should buy a new mouse. If it doesn't, you've probably got a dodgy port.
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