1. You don't need to reinstall ZorinOS.
2. The wrong thing is you have installed SH3D from software app.
This usually give unexpected symptoms. So, I recommend you to install SH3D from the official page (Download).
3. An alternative solution to your problem:
Use left Ctrl+Alt+Esc. This will change the mouse cursor in a red skull with two crossed bones.
Move the mouse over the frozen window and click on it. This usually kill the corresponding frozen process.