I have a 2007 Honda Civic and the radio display comes on, but no sound. Does anyone know how to fix this?

I have a 2007 Honda Civic and the radio display comes on, but no sound. Does anyone know how to fix this?

Added (1). I pressed and held 1&3 + power and display read FR L, not Diag. I went through all the speakers, but nothing happened. Display just showed:
FR L stands for Front Left Speaker
FR R stands for Front Right Speaker
RR L stands for Rear Left Speaker
RR R stands for Rear Right Speaker
ALL stands for All Speakers

The manual of the Honda Civic do not provide this information for user. There's a way to check the sound system or speakers for your OEM Radio: (Come with Honda Factory unit only.)

To enter the Diagnostic Sound Checking Menu, you have to Press and hold the 1 button and 3 button of your radio, and then push the PWR ( Power Button ). The LCD screen will display DIAG, means you are entering to the Diagnostic Mode. Press Next to go to each speaker position as follow:

FR L stands for Front Left Speaker
FR R stands for Front Right Speaker
RR L stands for Rear Left Speaker
RR R stands for Rear Right Speaker
ALL stands for All Speakers