My game has not been able to open for over 3 months. It crashes on start, doesn't even get to the loading screen. "unexpected error has occurred" I play off steam on a macbook pro

MacBook Pro (13-inch, Mid 2012)

2.5 GHz Intel Core i5

4 GB 1600 MHz DDR3

Intel HD Graphics 4000 1536 MB

It worked for a week then quit. 

I have tried changing launch options, verifying content and redownloading it. Please help or give me a refund....