Check your function key for sound. Usually on HP laptops, F9 is Volume down, F10 is Volume up and F11 is Mute.
First try tapping the Volume up button 5 or 6 times. If still no audio, tap the Mute button.
You may also want to go into the Control Panel and check your settings there. It is possible that the audio is not
being directed to the optical output. If no luck, then try re-installing the audio driver.