i had the same problem years ago. the problem is most certainly that you deleted some fallout2 files by accident and you dont have the folders but the games is shown as installed (when you look at the add/remove program list). but it doesnt have to be the same situation. the main problem is that your game is corrupted and you cant uninstall it. first of all, back-up your saved files somewhere if you plan to play with the same character. after that is done, you have to install a
uninstalling program. you can find such programs on the internet of course. such programs do the same what your
add/remove programs window does, they uninstall programs
entirely. when fallout2 is uninstalled, you can play again after you installed the game again
.