This KB will help you to address the issue with Windows being stuck at a black screen.
Such issues might also happen on a real PC, it's a Windows-related issue caused by the hanging of vital system processes or malfunctioning drivers.
1. Force restart Windows in Parallels Desktop: click Actions on Mac menu bar > Reset.
If you use a virtual machine in Full Screen view mode move the mouse to the top of the screen and wait for 1-2 seconds to open the Mac menu bar. To release the mouse input and access the top menu bar easier, press Control + Option shortcut.
Note: To avoid such issues in the future, we recommend disabling Windows built-in fast startup feature.
2. If resetting Windows did not help or the Actions menu is unresponsive, follow the steps from KB 6338.
REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal\MSIServer" /VE /T REG_SZ /F /D "Service"
REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\Network\MSIServer" /VE /T REG_SZ /F /D "Service"
net start msiserver
Then press Command (Win) + R buttons > in the appeared search bar type in devmgmt.msc > click OK, it will get you to Device Manager. Unwrap Display adapters tab, locate Parallels Display Adapter (WDDM), right click it and select Uninstall.
Reboot to normal mode and reinstall Parallels Tools.
4. If Windows cannot boot even into Safe mode or the steps above didn't help, Windows is considered beyond repair and a new virtual machine is required. Once a new virtual machine is created you can attach the broken virtual machine hard disk to the new one to transfer personal data stored on the C drive.
Note: Only files can be copied, programs should be installed from scratch in the new virtual machine due to Windows architecture peculiarities.