Unity crashes immediatly when playing a scene

Yesterday Unity suddenly acted weird when it was in play mode: I couldn’t get out of play mode, nor could I select anything in the project hierarchie, I could however still move the camera in the scene view.
I loaded a different scene, which did make Unity go out of play mode, but since then Unity completely crashes (almost) each time I try to play a scene.

Any idea why this happens and how to fix?

my collegues think it might be a caching issue, and suggest to clear the cache,
how do I do this properly? (because I don’t want to have to reimport the entire project, that takes hours)

what i think is there must be some loop in your Code which is not able to find its exit point. this loop continues to execute and that makes the game to crash. In my case I have faced this problem in case of loop.