Hello Rishiverma, I believe you have the same issue related to this topic,
I also am using dual boot. Windows and ZorinOS, sometimes I reinstall the systems.
First I install Windows and then Zorin, this because I want to make Zorin my main boot.
But always when I do the installing I first have to boot in to Windows and do some adjustments, after that I install Zorin.
I'm telling this because once I also ended up with a black screen while trying to boot Windows after installing Zorin, this because I did not start the Windows version and choose for restart and then install Zorin. I believe Windows needs to be in a hibernation form to make the dual boot work.
If you really want to remove Zorin, you can use the Windows install CD/DVD/USB to fix the mbr and boot back in to Windows. This action will override the Zorin boot records.
After that you can log in Windows and format the Zorin partition (I read you did the dual installation on same drive but seperate partitions). Hope this works for you.