Quick Solution: My iPhone is the same, i can here that its working and can use Siri to text and make all my calls, but the screen is completely black until it randomly came back one day. Now the same issue has happened again this is the 3rd time actually but I've figured out a way which fixes it instantly... . Just hold the home button and tell Siri to turn up your screen brightness and its back! . Only works for Iphone 4+ you may also need IOS7. So connect to computer and update then try again. Hope this has helped some of you.