No incoming calls ring on my iphone when locked ..

With the phone locked (with the power key) does not ring when they call me ..... but when the phone is not in lock or when in charge mode if it sounds ....
When I try to call from other phone gives perfect line but the phone does not ring until you hit the home key, or is in charge mode or the screen activated as I said before ....... the side button is not silent ..... I have everything right ....... I think this happens after I have updated to the latest version 4.2.1 .....
I can do? Help ......
Forgive for my English Greetings from Spain .... .......