Oh boy, a Microsoft update is causing problems again. Bleeping Computer reports the latest set of critical security updates that were rolled out last week can cause Windows 10 systems to stop booting properly after performing a system restore:
The issue affects all Windows machines where system protection is turned on and a system restore point has been created prior to installing one or more Windows 10 updates.
When users try to restore the system after the Windows 10 updates have finished installing, the system will not be restored and, instead, "the computer experiences a Stop error (0xc000021a)" and, after restarting the computer, the system will not be able to return to the Windows desktop.
Details on how to resolve this issue can be found over here. Microsoft is working on a fix.