This game is broken. Luckily, I like broken. I had an issue where Windows kept thinking the program was frozen, but I was able to work around it by enabling "Compatibility mode" (setting to "Windows 8" worked fine). My guess is that there's a bug in how you're using SFML that's prevent some sort of event polling. I also can't figure out Level 6, as I just go backwards. But I do like that I can just skip the first level by pressing ESC. Don't know if that was intentional, but that was interesting.