The first step is to run the volume control from the menu and make sure the sound isn't set to 0: it sounds silly, but it does happen.
The next is to consider whether you may have more than one device. Every motherboard has a sound chip, some video cards have one, some of us use USB speakers or headphones. The command "aplay -l" will list devices. If you see more than one (card 0, card 1, etc), then you need to make sure Linux is using the right one. Try running pavucontrol in a terminal: if you haven't got it, then install it with "sudo apt-get install pavucontrol. That will let you set the devices and basic volume for both input and output.
Last edited by DavidMcCann; 05-27-2015 at 11:30 AM.