Why is my project damage? or disapear?

Why is my project damage?, and even happens sometimes. I cant change de scene or project because the project disapear everything, until model 3D? how can I solved this problem?

I think what happening to you is you are modifying the scene when you have "Play" on. The button that you use to veiw your scene through the camera/game mode should NOT be toggled on when you are modifying your scene. Otherwise, the next time you toggle the button, all of your progress will be lost.

Therefore, when you press "PLAY" do what you need to see your scene then instead of clicking back to editor first toggle off "Play" then edit.