(SM5 Beta 3 on Mac OSX Mavericks) I Can't Use Enter T_T

firstly, sorry for my bad grammar .__.

Hi~ I'm newbie in this game and this forum ^^

I dont know whats going on but suddenly I cant use enter to start game. I might be press something in "option" and then I cant use enter/return anymore. I've tried searching in google even uninstall this program but it was useless u,u

what I supposed to do? I even dont know whats going on T_T

Please help me (_ _)

You probably accidentally unmapped the start button when trying to map your keys the way you wanted.
Find ~/Library/Preferences/StepMania 5/Save/Keymaps.ini and delete it to reset your key mappings to the default. You'll probably want to go remap them more carefully afterwards.
The Docs link says the directory isn't readily accessible on newer OS X and you have to use the Go To Folder... command.
People accidentally unmapping important things like the start button is why the key mapping screen was improved for Beta 4. Beta 4 hasn't been added to the downloads page yet, but it has a release thread in the News forum.