So, You have installed Windows after Zorin? Then windows probably deleted the Boot Partition. Depending on Your Setup and what You have done during the Installation maybe the whole Zorin Installation.
I would agree with @Forpli to try the Zorin Live Molde and use Boot Repair. And then You could use there GParted and takle a Look at the Partitions and if Your Zorin Installation is still there. Maybe You can make a Screenshot and post it here.
recently windows has been doing alot of shcanery they dont want folks who use windows to leave and goto linux so they do something to your windows install to prevent you from installing linux....they are scared if you do they will lose money from all the data they collect from you...windows isnt the product...YOU ARE!!!