Unity is destroying gameobjects itself

I am a beginner in game development, and I started following youtube tutorials to learn how to build a game. But now I am facing a big problem in it. The problem is that, whenever I press play button on Unity editor, it destroys all the gameobjects with main camera from hierarchy, scene view, and game view itself. So the game view is showing "no camera rendering on Display1". I tried to create new projects but the problem continues on every project. Even in the simplest scene with directional light and main camera only the stuff continues. I uninstalled and install again the Unity Editor. But again the problem appears.

Please help..!!!