This looks like a corrupted install to me, but you can try this before you take the giant leap of re-installing it: Try deleting your preferences folder. Note: This will delete your shelves, hotkeys, preferences, etc; so make a backup!

Back up, and delete "~/Library/Preferences/Autodesk/maya/2013-x64"

Now, re-open Maya, and if it asks you to import previous settings, click no. Check if it works now. If it does, great! You can rebuild your preferences (don't copy the whole folder over though, as you might hit the same problem). If the issue persists, copy the folder back, and let us know.

Best of luck.