Why cant I press + button and there's no sound

This means that you need to replace your charge port.. Your phone thinks it is in a dock causing it to try to output audio to a dock speaker when it is not plugged into one. The only thing you can do without replacing the charge port is to turn off the phone and put some rubbing alcohol onto a tooth brush (new and clean tooth brush) and clean the charge port with it. DO NOT use a lot of the alcohol. And let dry for 5 minutes before turning the phone back on. If this does not work then you will need to replace the charge port, which is a really easy repair and takes about 15 minutes with patience.