Any weapon, or any weapon with a charm quality? Do you have other equipment with a charm quality, and can you bring up the charm pane for that? Has Enchant Weapon ever worked?
There is a bug where the charm pane can open off screen. I have never seen any problems related to this except being unable to see the pane. However, try increasing the resolution you are playing in, if it is not already at 1024x768.
Just as a general thing to do for strange problems;
Try deleting all of the files in the '..\Divine Divinity\Run\Dynamic' folder.
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.
