Game won't save graphics settings.

Every time I restart the game, it's set to Windowed mode and the lowest settings even after I've reset it to how I want it. Has anyone else been experiencing this recently. It's really frustrating. I guess I could just set the settings to how I want it every time I open the game but, I shouldn't have to. It's never done this before. No, this isn't a problem because I updated to Windows 10. I haven't done that yet. I have Windows 8.1.