Numbers is compatible with 10.8.4
I suggest removing the preferences for Numbers by navigating to your users preferences folder using the menu item (in the Finder) "Go > Go To Folder"
enter the path "/Users/<YOUR_USER)_NAME>/Library/Application Support/"
then locate and move the files (but do NOT empty) to the trash:
Now restart Numners. If this does not work try opening Number while holding the <SHIFT> key to tell Number to skip opening already open docs.
Finally trash Numbers and reinstall from the the App strore