Posting the traceback would help. Each time you play the game it updates a log. If it has an error, it will appear in the traceback. If you are playing on mobile/Android version, then it might be a compatibility issue. Here is an example, (Nunu this is old for the 0.3 version)
I'm sorry, but an uncaught exception occurred.
While processing text tag {size = 72} in u'{size = 72}Your score is: 2128!{/size}'.:
File "game/script.rpy", line 918, in script
call screen endgamescreen
File "renpy/common/000statements.rpy", line 569, in execute_call_screen
store._return = renpy.call_screen(name, *args, **kwargs)
Exception: Unknown text tag u'size = 72'
There is more text but I'm just posting the bare stuff. we need you to post everything in the file here