When I go to make a call and hit the green "call" button, immediately my screen goes black. The call goes through, but I have no screen, so I can't hang up or open up my keypad to type numbers. The only way to end the call is for the other party to hang up. Then my screen comes back on. Could it be the sensor? But why only when I hit the "call" button. I have a Nexus 4 and updated to 5.01. I think my problem started before the upgrade, but not positive. Any help would be greatly appreciated as I am very frustrated right now.