*AFTER LOGIN COMPLETES AND LOADS* it only plays music and a tiny screen

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(Before I say anything else, I need to say, I have read ALL of your listed bugs and I cannot find a match to this.)
After the Launcher loads and signs in perfectly fine, clicking on PLAY only brings up a black screen with a smaller screen of minecraft in the bottom left corner, BUT it is NOT the login screen or anything else that has been described in all of your other bug reports. There are no buttons or any way to resize the screen, it simply plays the background music of the game and the small screen spins 360 degrees as if from a very far away and high up in the sky perspective, and there is no way to control any aspect of it. It will, if you do nothing, sit there and rotate and play music for hours. In fact the only thing that can happen is if you click on it, the small window will disappear and the whole screen is then black (meanwhile it is still playing the music).

What I expected to happen was...:
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What actually happened was...:
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Steps to Reproduce:
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