I had this problem and it turns out that for some reason (bug?) Limewire had at some point minimzed the window to an extremely small window in the upper left hand corner of my screen. I would have never noticed it had it not been for another forum user (jstern).

Take a look and see if that's the problem. It was literally reduced to a line that is only 1 or 2 pixels wide. If you see this line, drag it open and you should be good to go.

Good luck.