If you’re using pulseaudio, open the pulseaudio volume control (pavucontrol in a terminal). You should be able to unmute and set your volume from there.
We have to unmute everything and increase the volume. Press M for toggling mute/unmute. Use Up and Down arrow keys for increasing the volume.
Also there is a volume icon at the top right. I use XFCE DE. Not sure about other DE though. It is volumeicon. Right click on it–>Preferences–>Change the hotkeys and enable it and change other settings you need. I enabled the hotkeys and the horizontal slider.
There is this thing called as pavucontrol (Pulse Audio Volume Control). It is a GUI for pulseaudio. You can change the volume to the necessary level here too.