Hi there eatall, is this the first time trying to play the game? If you've played it before, then it might be an issue with your persistent data. There is a fix for it.
Disclaimer: The fix requires going into your %appdata%. Please only do this if you know what you're doing. I am not responsible if you damage your computer.
1. Visit your %appdata%
2. Look for the folder Roaming > Renpy > CampMourningWood
3. Delete the 'persistent' file inside this folder
4. Try booting up the game now.