Ipad screen turned black

I was using Youtube through Safari. I clicked a video and made it full screen and then the screen turned black. It didn't show me the usual appearance of a video in Youtube.(the pause button, the progress of the video,etc) Although the games and the apps still work. I tried closing it first then opening it again. when i went back it still shows a black screen with the word Ipad and the time. Does anybody have ideas on how to put it back to its normal self? Please HELP!!!!