Try browsing to the '..\Documents\Larian Studios' folder and renaming the 'Divinity Original Sin' subfolder.
This folder contains the saved games, configuration files and a level cache folder. Deleting or renaming it will get the game to recreate it on startup; playing the game from a different Windows user account would effectively do the same thing.
After that, start the game, create a new profile, and see if you can save a new game and load.
If that works, try copying a few of your saves from the renamed folder to the newly created profile's savegames folder.
