Hi.
Well.. thats a really strange problem.
First thing to try is:
_Reinstall! Make sure you back-up your saved games first.
_Install the game again with TotL. You can find it here
http://www.planetbaldursgate.com/iwd/info/luremaster/
The TotL expansion is the *only* way to get the latest patch. DONT INSTALL ANY OTHER PATCHES. Your order of installation should be:
IWD
HoW
TotL
Another good this would be to turn off 3D acceleartion in the game configuration. I remeber it causing me no end of problems on a TNT2 card.
If this dont work let me know.