@RedDoggie from that grub> prompt, type:
exit
What do you see when you do that?
If no option for Zoin, from your Zorin installation Live USB, look for "Grub Repair" or "Boot Repair Disk".
Run that and see if that fixes the Zorin boot issue.
Some similar problem discussed here: Installed Zorin and all I have is a Grub prompt!
(but that user was dual-booting alongside Win 10)