If you hover the cursor over the damage range, it always lists 2 as the component from primary stats? A club should get all of its damage bonus from strength, a sword get most from strength and some from agility, a bow gets most from agility and some from strength, while a knife get all from agility. It sounds like the game thinks everything is a bark or willow, which can get a damage bonus based on intelligence.
Try removing the weapon and shield completely and see what is listed for damage. After that, equip a sword or something, and see if the damage remains as before.
Try deleting the files in the dynamic folders;
'..\Beyond Divinity\Acts\Act1\Dynamic', '..\Beyond Divinity\Acts\Act2\Dynamic', etc.
These folders are used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied to those folders when you save a game. The files will be re-created as required the next time you start Beyond Divinity. If there was a corrupt file in those folders, deleting the files should fix the problem.
