Re: Sims 4 play button won't highlight.

Try these:

The Play button in Origin is gray

Make sure your game is updated to the newest version (see above). If that is the case and the play button is still gray, try the following things (or any combination of it)

• Restart Origin
• Manually uninstall Origin, run ccleaner, then reinstall
• Right click on the Game in Origin and hit Repair Game
• Log out and back in
• Delete Origin cache files
  
  Source: http://answers.ea.com/t5/The-Sims-4/FAQ-Installation-Updating-and-Startup-Issues/td-p/4276949