First, the official greetings
Welcome to GameBanshee! I hope you enjoy your stay here.
Then to the problem:
Have you tired to reinstall the game with humongus install? I mean, uninstall the game and install it again?
As for removing SP2 (Service Pack 2), as far as I know (haven't ever done it myself) it's much trickier thing to do, and if done wrong may mess up something in your computer. So if there is someone who has more experience with removing SP2, please give the details.
So, all I can suggest to do while waiting for those instructions is to try several times reinstalling the game with humongus install. Also, you could try if selecting smaller install helps.