It's possible that you've changed the zoom level of your project. You can see current zoom level in the lower right corner of the screen. In zoom mode, you can see a wider view of the project, but controls are disabled. To return to normal zoom, click View>ZoomToNormal. This should make the controls accessible again.
Thanks for the clarification J3627. I'm not sure why these options were removed from the menu, but the keyboard shortcut is still functional, as you noted.
