g'day theresa, and Welcome to Linux.org
Tell us more please.....
Has the sound always worked ?
do you listen through speakers or a headset ?
What happened immediately prior to the sound stopping?....power loss?....updates?...anything at all...
Do you have Timeshift installed and set up ?
Have you checked the connection for your speakers/headset ?....
Click the sound icon in the clock area and make sure it is not muted.
You can also access 'sound' by clicking on menu and typing sound in there