Do your mini and auto maps display the correct surroundings? Does the menu bar, inventory pane, etc. show up? Is your desktop set to 16 bit colour? Have you tried running the configuration program and switching to software or DirectDraw mode?
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.
After this, start a new game and see if you can go up and down stairs (the cellar of the house just south of the graveyard would be easier to get to than the catacombs). If a new game works, but your latest save still does not, there may be something wrong in the saved game. If neither work, it may be a problem with Divinity itself.
Someone ran into a similar problem in the topic
Small game?