E2420H, completely Black Screen

I just connected a brand new out of the box Dell E2420H monitor. I have a 3 monitor set up and replaced one of the older monitors.  I connected the DP cable and the power cable, booted up my computer and everything worked fine, didn't miss a beat, all morning. After about 4-5hrs of everything going fine, all of sudden the new Dell Monitor went black......completely black screen (white power lite still on). I sat back from my desk for a minute and thought what the heck happened. After about 1 minute, it just came back on and was fine for about an hour. Then all of sudden black screen again. I played with cords & cables and nothing changed. I finally unplugged all the DP & Power cables from it and gave it a minute or two and then re-connected everything, and it fired back up and worked fine for about another half hour. Then it went black again. I changed the DP cable, and the Power cable, I disconnected and reconnected them, I rebooted my computer and still nothing. Only the power light comes on, otherwise you would think it was still unplugged.  Is there a setting or something that causes it to go black, or should I just return it?