I have been battling this problem for over two years (since version 14). It has been frustrating, to say the least. Every time the solution has been to remove parallels, and restore a time machine backup of the VM. I have tried everything in this forum with no avail. I agree with other users, I believe the instability lies between Microsoft updates and the hypervisor running away with host resources. I own my own business and have lost countless hours on this particular instability. When Parallels announced v16 today, I almost took the suckers bait of "they had to fix this" in a major revision release. I couldn't take the chance. Over the weekend I removed Parallels and installed VMWare Fusion. It lacks the bells and whistles, but is a no-thrills stable VM host. Parallels lost a long time customer today. I have been running their software since version 12. The frustration I encountered myself and those in this forum was enough evidence that it was time to move on.