Everything on Hierarchy is gone execpt main camera

Hi,

Today I noticed that everything created in Hierarchy is gone. Det only thing showing is Main Camera. The same thing for all my projects. The same thing happened for the example project I downloaded a while ago. It worked before. Now the only thing left on Hierarchy is main camera. I have downloaded the example project again, but the same result. Does anybody know what has happened? Thanks in advance.

Sometimes downloaded projects will have multiple scenes, and a default one will not be open. Find the scene and open it, that is where the hierarchy should be. Same for your own projects, look for the scene and open it.