taytaylewlew11 This is in a new admin user account on your Mac? It looks like there's some kind of overlay getting in the way. What other apps are running at the same time? If you're not sure, click cmd-optn-esc and list everything that shows up. You should only see Sims 3, the EA App, and Finder. You can also use this function to quit the game if necessary. Use the up/down arrow keys to select the app you want to close, and click Return to tell it to force quit.
If you don't have any other apps running, or closing them doesn't help, try putting the game into windowed mode. Clicking cmd-return at the Main Menu should do it. But if not, open Options.ini, inside Documents > Electronic Arts, The Sims 3, click cmd-F (Find), search for fullscreen , and set it to 0 (zero).