problem with new droid

So I finally got a replacement Motorola Droid for my original which I had since December. Seemed no one could understand me when talking. Verizon sent me a new re-conditioned phone for free. The problem I'm having now is while I'm on a phone call the screen goes black or asleep and I cant see anything or get it to come back on. I've tried to push and hold the power button, I tried to slide the screen open and still nothing. The only way I can get it back on is to plug it in, then it comes on. Hope I described it well enough. Thanks for any help...Mike

 

That's how my old one was...it would time out and I would hit the power button and the screen would come back showing the end call screen. Now I can't even end call, when I hold the power button in nothing happen no screen no power off choices. Once I put the AC plug in the screen appears and it works fine...

 

Quick update. ...Verizon Rep sending another phone out. Said the problem sounds like something wrong with the sensor that turns the screen off when you put it to your ear. He was more upset that the phone was sent out to begin with having this problem