A mod ruined my Oblivion files, so I uninstalled it and reloaded. Now I get a blank screen when I start a new game. Must I delete the Save folder and start this over too?

Have you installed the game again in the same location/folder? If yes, then have you removed "remains" before installing again?
I don't think you need to remove saves, but it's a good idea to remove Oblivion.ini from My Games\Oblivion folder.

Thanks! I'll give it a try.