oblivion not starting

[343 guilty caboose]

All I can remember is deleting a mod sound file from Oblivion/sound (not Oblivion/Data/sound)

[Vagrant0]

No; and yes. All important files are stored in .bsa files.

Except that the files in the BSA will no longer be used if something in the data folder has overwritten them, and you are using a saved game with those overwrites in place.

 

Since the game isn't starting, the only real solution is to do a fresh install, and only add the mods that you want to use. You may not like the idea, but sometimes, due to what mods add or change, this is the only solution. This is especially true since you were using a .esm which probably wasn't entirely self-contained. You may have also accidentally deleted some of the files needed by the vanilla game by accident. Not everything is stored in the BSAs.