Target window gone
 

I've lost my target window - on ONE character only, adn only in Fullscreen mode. Alt-T does nothing.

Suggestions?

I would try reloading the UI from the options menu and/or doing a full computer restart to see if that resolves.

It's probably got positioned off screen somehow, so even when you hit ALT T it hides/shows off screen.

If you're masochistic you could edit the appropriate XML file to fix it, but by far the simpler/faster solution will be what Warpath said:

Is there a check box in the options window?

If a window is offscreen, you can do /load and uncheck 'Keep Your Layout' and it will reset the UI windows to default positions when you reload it