Could you please send us your log and save files so we can take a closer look? You can find them here:
Windows:
%USERPROFILE%\AppData\LocalLow\Free Lives\Stick It To The Stickman\
Send them to support@freelives.net
In the meantime, try verifying the game files in Steam and make sure your graphics drivers are up to date. This often clears up black screen issues.