Right click speaker icon in the notification araea, icon next to date and time. Then in the open window select playback devices and make sure your external speaker as set as default. If speakers don't show up, rick click in an open area of the playback menu and select "show disconnected devices".
Hopefully there is some setting you need to change, but I had a Dell once that the left speaker never worked, although both headset channels worked. Turned out to be a motherboard problem. Prior to realizing what it actually was, they changed the internal speakers first, if you are referring to internal and not external speakers.
You might explain what was going on when the speakers quit working? Were you playing something at the time?