Default HTC HD2 black screen during a call

Hi guys, I've a problem with my HTC HD2.
When I make or receive a call the screen turn off and I can't do anything, I can't use the speakerphone or keypad, nothing at all.
If I want to close the call I must unlock the phone and hang up by navbar.
I've searched on web and I found many thread in relation to my problem; I've tried many solutions to resolve it but failed.
I've also disabled the light and proximity sensor but it didn't work. The problem still remain.
I've forgot to say that I changed the main flex and the display of my HD2 because the originals was damaged. Until now I never had any problem, it all started with the new pieces.
I tought that if the sensors were damaged the screen shouldn't become black when I answer or when I start a call, am I wrong?
Another thing, I've just inserted headphones in the phone and made the call from another device: the screen remains on and I can use all the commands without any problems. What could be the problem?
I hope someone can help me to find and resolve it.

Ps: I apologize if there are mistakes in my english but it isn't my mother tongue.