I had the same problem. My screen broke so i have been trying to replace. The glass on the proximity sensor fell off and then the it stopped working. So i thought that the proximity sensor was dirty or broken and it wouldnt work. So i found out that the problem was because of the rubber plastic that surrounded the proximity sensor. So i cut a rubber piece of a ear plugs and cut a tiny little hole around it to place it right around the sensor. And immediately it startes to work. It was a very thin slice of rubber. I use the ear pieces of rubber of one that i wasnt using it and it worked.