No sound Output Logic Pro X

No sound output on logic pro X.

I have been trying for a day and a half to solve this and watched countless videos/read posts. I can input sound (and hear it) through my presonus audiobox USB96 and record, seeing the signal and waveform in the record bar. When i try to listen to playback - nothing! I have tried:-

matching audio output device to audiobox/plug in headphones/built in speakers - nothing

checking and unchecking core audio

checking software monitoring and auto input monitoring (and switching off auto input monitoring when trying to listen)

rebooting system (several times!)

transferring the file to my Imac from my macbook and repeating all the above - no joy

Am I missing something obvious (and no the mute button isn't checked!)