There are two possibilities. The first is that you opened the After Effects Render Engine instead of After Effects.
The second is that you have fouled up a Workspace, so the Reset option does not work. You can solve that problem by opening another workspace or by just going to the Window menu and looking for the Composition panel name. It will be right after the Wiggler panel.
I think that opening the Render Engine is the most likely cause of your problem.