Green, please try to be specific with relaying what you see.
We cannot see your screen or see the details. It is up to you to relay that information.
If you are trying but not succeeding at restarting the computer- please explain what it is doing that presents a restart. Normally, the power button works.
Normally, rebooting will get you "Un-frozen". Trying to fix a crash During a Crash may cause file damage and corruption.
How to Quit?
Reboot is working, But as soon as I login the Screen Freezes!
Just Try a Restart Now!
This may be caused by overheating - we should check that later...
For now, can you reboot - then once you see the Motherboard Splash screem start tapping the esc key to pull up the Grub Menu.
You should see Advanced Options for Zorin
Select that, then select Recovery
From the Recovery menu, arrow key down to Enable Networking
Once enabled, back to the Recovery Menu and arrow key down to drop to Prompt
Hit Enter again...
Then run
sudo apt update
sudo apt install --reinstall zorin-os-desktop
This will include GDM Display manager which is crashing upon login.
Once that is reinstalled, back out of the menu and proceed to normal boot and test..
Able, to Login but seeing a Black Screen!
Press Ctrl + Alt + t
to open terminal then as @Aravisian said
sudo apt install --reinstall zorin-os-desktop
Are you using Nvidia or AMD Graphics?
What card?
Desktop is back 
Ok, please immediately run
sudo apt update && sudo apt full-upgrade
Once completed, open Software & updates and move to the Additional Drivers tab.
Please relay which drivers you are using for Nvidia- and which Nvidia card you have.
GeForce RTX 20 Series
Ok, so you should be on the 510 proprietary or later drivers...
@Aravisian Already done, No updates.
@anon6471198 rebooted again to check and everything is back normal.
Thank You Very Much
by the way what went wrong in my PC?
Some Sort of Rogue Application was making the OS crash, still no idea how you identified it so quickly
Then we installed the Desktop 
Currently,
sudo journalctl -b -1 -e
Has not been run to review the logs. You have not relayed which Nvidia Driver you are using.
It's hard to be certain.
however, since reinstalling the desktop helped - I would guess that an essential file was corrupted during a recent update perhaps due to packet loss during download.
I guess So?
I tried Update & Upgrade, nothing there as I said
but it worked, I can work with that
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