Hi, Simon.
Thank you for reaching out! I'm happy to help!
My first suggestion is to locate your project (.story) files. By default, they are saved in your My Documents folder, under My Articulate Projects. If they're not there, you can search for any .story files in your local drive by typing ext:.story in the search bar of Windows Explorer.
The next step is to do a quick repair of Storyline 3. You can follow the instructions in this article.
If you are still having launching issues after the repair, I'd recommend opening a support case with our engineers.