Second, make sure you really did make a copy of your wallet.dat file and that it's in a location you can retrieve it later. This is very important. You lose this, and your coins truly are lost.
If your user name is MstrMynd, you'll find your wallet (and all other related files) here:
Open a terminal window and type this:
That copies your existing wallet to your desktop.
Now, to completely uninstall the application, drag it into the trash. Then, delete the contents of the folder above. You DID save your wallet.dat file, right? If you didn't now you've truly lost your coins. In the same terminal window, type this:
Now, download the latest Bitcoin Core client (v 0.11.0). Drag it into your Applications folder as usual. Start up the application. It should connect and start downloading the blockchain again. Yeah, it's going to take a while. Once you actually have some connections, stop the client. Copy your old wallet.dat file back into the folder:
Launch the Bitcoin application again. It'll continue downloading blocks, and when everything is caught back up, you'll have your coins.