Hopefully this will help someone with the same problem. The specific issue I am talking about is the situation where a windows virtual session periodically goes black and becomes unresponsive in parallels. The cursor disappears, and even if you bring it back up, it goes away again immediately. Trying to stop or reboot the windows session from the "action" menu does nothing. Closing parallels and restarting does nothing. Reinstalling another virtual session is possible, but time consuming, and the black session will remain in the control panel.
If a virtual session goes black, the following solution corrects the problem every time:
1) Right click the parallels app in the Mac menu bar at the bottom
2) Click "control centre" from the menu that comes up
3) Control centre appears and shows any virtual sessions running. right click on the virtual session that is frozen with a black screen
4) A menu will come up with some options. Select the "stop" option. Click OK on any warnings that might pop op. This should shut down the session properly. When session is completely shutdown, proceed to next step
5) Re-launch the virtual session that was previously frozen. it should boot up normally and be back to full function. A windows update may be required periodically but should happen automatically.
I believe the black screen appearing in the virtual session has something to do with battery monitoring, screen saver, or related, but I cannot reliably reproduce it. I routinely leave the session running for weeks at a time, so that may also have something to do with it.
Anyway, the above method fixes the black unresponsive session every time and doesn't take too long. Annoying, but workable for the rare time it happens.
Hope this helps someone. Took me forever to solve this one!
