I think there's an icon in your ootp folder to unlicense.
But yeah, comletely get rid of ALL evidence of ootp, including the install file. either re-d/l the install file, or if you have a hard copy of it on cd, just use that, and just start 100% fresh.
Oh, and DO NOT change the default directory either. leave the default the default. dunno if that has anything to do with, but I do know it installs in 2 different places, one in My Documents, and one in Program Files. The one in My Documents is where all the mod files go, and the one in Program Files are generally the stuff you don't wanna mess with a while lot
Sim City 4 does the same thing. I changed the default directory, and kept getting crashes (especially after I d/l a bunch of mods) I think the computer was trying to look for the mods in the directory where it was SUPPSOSED to be, I have no idea, I'm only speculating at this point. Anyway deleted everything, and just put the game in the default directories and it works fine.
With ootp, I never changed the directories, even the first time through, so I still don't know what happened with my first install on that game. All I know is that it works now the way it's supposed to
Again, I'm only speculating, but it's defintilly wort a shot.