try Plug in speaker and restart your computer.
I removed my external speaker for half a day and then replaced it to find no sound. Sound only issues from the internal speaker.  The Troubleshooting message says 'speaker is unplugged'. I have checked the speaker and lead on other devices and there is no problem. All the sound jacksockets give the same message. The computer is an Inspiron 3668. I'd appreciate suggestions of a way forward. Many thanks.
Jackplug not recognised