Ctrl+Alt+T , to open terminal/command line. Type
alsamixer, hit enter. This will bring up Alsa Mixer application.
Do you see
Auto-Mut part? Do you have it enabled? If not, speakers won't be muted. Using left/right arrow keys navigate to it, and using up/down, enable this option.
Do you see your line with a vertical bar? What do you have bellow? If it is MM, it means your headphones are muted, so no sound will be comming out. Using right/left keys navigate to headphones, unmute them by pressing m on your keyboard, up/down arrows bring the volume level to desired percentage. Master volume is also important - if you have that muted or at 00, nothing will come out. Change it just like I already explained
For some reason 14.04 version ships with volume muted by default, which is very weird. Had that issue when installed on chromebook and when updated on my Toshiba laptop from 13.10. Pretty sure Auto-Mute is disabled by default as well