I'm thinking along the same lines as Othesus, in addition to it possibly being a transparency/opacity settings (which are controlled via the Window Settings that Zyther was referring to. Try cycling through the F10 displays like Othesus mentioned then pull up the window settings of the inventory window and check the trans/opac settings (assuming, of course, you'll be able to even
see the inv window when doing the "F10 Shuffle"
