I start the game, and my mouse pointer comes up, but it doesn't highlight anything on the screen when I scroll over, and clicking does nothing. Left click, Right click, Middle click, Buttons 3, 4, 5 or 6 do nothing. They work on my mouse diagnostic program and in other windows. It works on LoG II. I can use the keyboard to navigate the menus, but I can't manipulate the check boxes. This happens both on the Steam version and GoG version.

Windows 7 Ultimate SP1 (x64)
Logitech M705 wireless mouse.

EDIT: Uninstalled, reinstalled, restarted computer, to no avail. Changed Mouse. No dice.

Found the problem to be GeDoSaTo messing with the mouse cursor position. Removed Grimrock from the Whitelist and presto.