Playback not working & no sounds loaded in mixer

Hi folks

This seems to be a file specific problem as it's not happening on other projects, but on this particular project no sounds are loading and no playback is happening - I just get a static blue bar at the beginning of the piece. IO preferences is set to 'default' and - nothing. Audio device is set to 'system default' in the IO tab of preferences. Have also switched that to 'built in output' and still nothing. No sounds loading in the mixer either - I'm assuming that THAT is the main problem, but I don't know how to fix it... I'm on MacOS

Any help please?
J