In grub menu select Advanced options for Zorin and then select an older kernel (not a recovery kernel) to boot from.
If your grub isn't displayed at boot, press continuosly esc, tab or left shift key (the key depends on your hardware) to show the grub menu.
Moon, it happened to me as well. Just use that Advanced Options they are talking about, and don't go updating to 7, or fooling around trying to fix Grub.