I bought my iPhone on Sunday. Two days ago, I set the ringer volume all the way down but reset it back to a level between mid to high. All it's doing now is vibrating. if I turn off vibrate, it doesn't even do anything and I'd never know someone is calling if I wasn't staring at the phone. If I change ringtone, I can hear the ringtone. However, the key sounds are no longer working either. Did I press some button that disabled something?