I had the same issue for several weeks which persisted after upgrades to High Sierra / Parallels 13. Reinstall of Parallels Tools, Windows restore, etc, did not work. Per other users, the solution posted by MikeS14 on this thread worked for me: https://forum.parallels.com/threads...r-freezing-task-scheduler-crash.340605/page-2 To summarize, - Start Windows PowerShell or Command Prompt (once the start menu finally works) and type "regedit" - Navigate to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\Maintenance\State - Under "ReportedState", change from 3 to 0 - Restart This temporarily fixed the problem but the bad behavior came back several days later. I reapplied the fix and did various Windows updates (don't remember the exact order). The value of "ReportedState" now shows 1, "Control Panel"->"System and Security"->"Maintenance" section now allows "Start Maintenance", and things have been stable for a couple of weeks. Per MikeS14 this is "at your own risk" and possible side effects are unknown, but the system is behaving for me now.