@dnob Hi and welcome to the Forum.
I wonder if this item will help: Zorin OS 15.3 OS Ultimate on Asus Laptop VX2S Nvidia - blank screen
There have been a few problems recently of black screens but none which look like startup loop like you seem to be seeing.
If the worst comes to the worst and you decide to re-install then if you use “Something Else” method you can choose to NOT Format your /home partition. So your data stored there will not be disturbed.
Lets see if between us all here we can get you fixed and avoid a re-install.
PS: Which version of Zorin do you have e.g. Core or Lite.
If Lite 32bit, look here: Black screen after update