Possible Bug ?

I ran into an issue where my screen was black (not the entire screen just the display screen which shows yours work) i could check my time line and everything else which was working fine and i also rendered out my animation which turned out to come out alright and the image was there however even when i left after effects and came back the screen was still black and i even tried emptying the disk cache but nothing. Not sure if its a bug or not it happend as i was animating and then i took a step out and came back and it was frozen (nothing moved) then i exited out and came back and the screen was black.