You just have the application window stretched to be too wide to fit on your screen---probably because you are using a workspace saved for a wider monitor.
It looks like your screen resolution is not set wide enough or your app frame is not centered. The outline of the Stop is there. Try undocking the Panel or resetting the workspace. If that doesn't do it make sure your display is set to the minimum required by AE.
Thanks Todd, that was it... I figured it was something stupid. I use AE only a few times per year.