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I have one possible solution but USE THIS AS YOUR OWN RISK!! I will not take any part if your computer doesn´t work after this!!
1. First backup your saved games, portraits etc. which you wish use later.
2. Delete your BG-folder
3. Open Start- menu and select Run and write " regedit"
4. Go to HKEY_LOCAL_MACHINE and there you open SOFTWARE and delete Baldur´s Gate folder.
5. Then try reinstall your BG.