Thanks, I deleted the files. I also tried installing and uninstalling another game, and that works. The morrowind-installation completed successfully before - but now I'm tired of talking about Morrowind lol.

In the future, when I get Morrowind, I want the following mods:

MGSO - makes the game prettier and includes the code patch apparently
Tribunal Delayed
Solstheim Rumour Fix

Okay, I think that was it. Thank you, heroes, for helping me in this difficult quest! :D