An update from this post
In brief, system is a legacy 5 year old ACER notebook with security turned off.
Began with a regular "Sorry Zorin has experienced some error etc."
I had been getting this message for several months and decided Boot repair was the answer.
Boot repair initially asked for terminal commands, which failed with holding broken packages. BR closed leaving me grubless. After help from @Aravisian and surfing, BR eventually stated the system was GPT and to add a 1+ esp partition.
I duly did so, BR seemed happy.
Now I am stuck with the no media error.
After a day of searching and experimenting I am still stuck.
Seems two ideas:
1/ Bootloader not being read / missing
2/ dead drive - hope not, it is only circa 18 months old with a few dozen use hours
My impression was BR DID install grub2
Is it possible that somehow I have messed up the ESP partion (at the start of SDA2 and system is trying to read from that?
So before I do this for the nth time, can some kind, wise soul please link me to a site with pictures that shows me step by step, holding hands, how to set up this wretched SEP partition. ( although I still can't see why I need it when I did not before and the system is Legacy!)