Quit the app completely and restart the iPad.
Go to the home screen first by tapping the home button. Quit/close open apps by double tapping the home button and the task bar will appear with all of you recent/open apps displayed at the bottom. Tap and hold down on any app icon until it begins to wiggle. Tap the minus ➖ sign in the upper left corner to close the apps. Restart the iPad. Restart the iPad by holding down on the sleep button until the red slider appears and then slide to shut off. To power up hold the sleep button until the Apple logo appears and let go of the button.
If the videos screen is still black, try this.
Swipe to the right from your first home screen to get to the iPad Spotlight search. Type in the name of any of your movies in the field at the top. when the movie appears in the search - tap on it and it should hopefully start to play. Let it play for a minute or so - hit done - go back to videos app and see if all is OK.