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 D:OS, create a new profile and see if you can start a new game and save/load. If so, try moving some of your current saves, if applicable, from the renamed folder to the newly created profile's savegames folder.
