Need basic advice please

My student was on the final stages of her audacity assessment when suddenly all her tracks have’ flattened down’ and no sound can be heard. When I go back through her history, she plus zoomed, removed some faults and then imported a new track. At this point the new track could be heard (and sound waves seen) but all the older tracks can no longer be heard and appear as flat blue lines.
Hope this makes a smidgen of sense!

Is Audacity running on a network? Is the work on network connected drives?

Which three-digit Audacity version is it and what kind of computer?

Koz