It's a Microsoft mouse? Open Windows, throw mouse thru, close Windows.

Really if it is only a few weeks old, return to store. It will probably act up again no matter what you try to do to fix. Yes, the cheaper ones work just as well. I look for the specials that offer a rebate that makes the price ZERO. I keep one or two on hand and if the one I'm using goes bad, open Windows and... you know. Then get out the next free one and use it untill...