I bought a second hand iPhone 4. It is in a very good cosmetic condition but there are some problem with the hardware: the camera doesn't work (shutter won't open) and the mute switcher does not work, too. And it's not over. When the phone is ringing or I'm playing with any game there's no sound. But the speakers work well when I'm browsing on the net or seeing video on youtube. How could I fix these problems or at least one of them? Thanks in advance!