When it works, you are the cannon, but it happens at least once a day, the screen goes off and start again, being so in a few minutes.
Got a new screen sent by Dell after talks with their support, but it was the same problem. Tested with another computer the same problem.
Googling U2715H goes black before the purchase.
NOTE: The above applies to display mini display port cable that comes with. Have now used the screen with HDMI in a month and everything works as it should.