Are you sure there is something onscreen to highlight? Try dropping a potion or piece of equipment, and trying again. Did you shut down all non-essential programs before starting the game, and possibly re-booting before that? If it really is broke, try deleting all of the files in the '..\Divine Divinity\Run\Dynamic' folder, then start Divinity, create a new game and see if alt is working, or not.
This folder is used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied from that folder when you save a game. The files will be re-created as required the next time you start the game. If there was a corrupt file in that folder, deleting the files should fix the problem.
If a new game works after this, try your latest save. If your save does not work, but a new one does, there may be a problem in the save game folder itself. If neither work, it may be something with the game. If this is the case, you could try re-installing the game. Zip or otherwise backup your saved games folder to another location first, just in case. Then un-install, re-boot, shut down all non essential programs (especially anti-virus), re-install the game, perhaps start the game and see if the problem persists (usually not necessary, but would help identify problems cause by the patch), re-boot, shut down all non essential programs, install the patch, re-boot, shut down all non essential programs, start the game. This procedure is a bit over-cautious, but the best way to avoid install problems.
