First, try this patch that is ToB compatible:
http://downloads.bioware.com/baldurs...98_ENGLISH.exe
That is the official patch for Throne of Bhaal and Shadows of Amn combined. Then, after downloading and running that, do this one:
http://baldurdash.org/LargeDownloads...FixPack112.exe
Install that fixpack, then see if your game works. If all else fails, check to be sure that you have no software compatibility issues with the computer you have. Good luck!
-Brainless One