Try this first. It happened to me and drove me crazy until I accidentally discovered it. It's actually on the screen but "off" the screen at the same time. It happened to me after I'd made a really big render and then back down to the normal size.

Problem is, I don't remember if I found it by going to the larger size or scrolling to it by making the poser interface sometime less than full screen; but it's there. You don't need to delete or re-install.