

You'll eventually find the one that's corrupt. If it's the config files (i.e./ your project folder.gmx is intact and has everything inside), make a copy of your project folder (as a backup), create a new project in GameMaker, save and close, and then try to copy the folders across one by one, open the project after each one to see if they're loading into it. This, my friend, is why you keep your own separate backups. When you say it won't load, what do you mean? Are all the files still in the project folder? If so, the config files are probably corrupt.

System Restore doesn't effect personal files, so won't save you here.
