Unplug it. Take the top off. "Fish" for stuck papers with an unwound paper clip, preferably a long one! Sometimes, you have to help the leftover stuck pieces move along. Thus, remove paper clip, plug it back in, and try shredding some papers. If that doesn't work, fish some more!
Unless, of course, the paper is too wet to be fished out.
Many days of paper-fishing because I didn't empty out the bin enough!
These shredders are designed to be replaced often (so they can sell you a new one).
http://www.brokenshredder.comTake care..