Lost sound on all audio tracks

long shot ...

with project open, use ctl-a to select everything on timeline; in the audio properties [right side] reset gain to 100

does that help?

if not, suggest you contact free tech support

As a first troubleshooting step, have you tried playing another audio file to make sure there isn't a problem with your computer's sound system?

Hello Linda;

While Camtasia is open (and there is audio on the timeline) please right-click on the speaker icon in the lower corner of your computer (on the taskbar) and go to Open Volume Mixer. Please verify Camtasia is not muted/turned down.

https://www.screencast.com/t/kCgRoHKDHeH4

-Robert

Ive had this happen to me in the past, not fun!
 
1.  Hopefully you were able to save the most recent copy of the project. 
as a hint, and because of a lot of lost mid project work, I get in the habit of saving probably more than I have too.   
2.  If not, you may need to rebuild it.  However...

In my case it was more of a PC memory issue.   I had a lot of other files, and programs open, and I am no techie, but I just got a sense it was a memory issue. Same as you, shutting down just Camtasia had no effect.   A hard reboot of my PC and the when I came back the sound was back!  

Not sure that makes any difference at all?   I just don't love Camtasia's built in audio editing tool for basic stuff it's fine, but I seem to have better quality using Audacity. 

Not sure you have this on?  But it's a nice feature.

Back up a Project Automatically (AutoSave)

AutoSave automatically saves a backup project file for recovery. AutoSave is enabled by default and is set to save every two minutes.

To Change the AutoSave Interval

1. In Editor, select Tools > Options > Program tab.
2. Make sure the Enable AutoSave option is checked.
3. Enter the number of minutes between saves into the AutoSave interval field.
4. Click OK.

If you open the project after a crash or system failure, Editor automatically recovers the last saved project file.