Hmm, interesting. It could possibly be a bug with the game's save registry? Try opening your registry editor and go into "HKEY_CURRENT_USER\Software\OmegaOzone\Dungeon Tail". Once you're there, try deleting everything in there or just delete the folder and then see if the game works or not. Let me know how it goes!
Actually I thought about investigating it myself and I managed to reproduce it. If you save at the narrating black screen after the camp setup scene "A short stoll later and etc.", click to continue and then close the game, either by using the main menu or killing the process will bug out the game. It's not only the registry tho. To fix everything back up you need to delete the registry directory, the Appdata/LocalLow folder and maybe the AppData/Local/D3DSCache folder, not sure if this one is from your game or not and maybe it was pure luck but this made everything work again, I also made a clean folder with the game just to be sure.
EDIT: At this point I'm curious if you can corrupt the game at any narration scene.