After installing a few recent updates[1], a Windows 20012 R2 server demanded a reboot. Instead of coming back normally it got caught in a reboot loop with error 0xc000021a. The following was attempted but with no success:

  • repair mode
  • last known good
  • safe mode

Most finds on the internet seem to match XP/2000/2003 instead and provided no help. What can be done (short of a complete reinstall)?

[1] I'm not 100% in reconstructing this, but according to what my WSUS reports as "downloaded" for that box, I suppose the updates were KB3084905, KB3094486, KB3095649, KB3095701, KB3096433 - just in case that's helpful.

  • 2
    You could...... restore it from backup.
    – Ryan Ries
    Oct 29, 2015 at 17:23
  • You need to boot up to an install disk so you can access a command prompt and view your logs to determine what's wrong. Or, as suggested, restoring from backups should be quicker and easier. Oct 29, 2015 at 17:59
  • @HopelessN00b Sounds reasonable. Since the last reboot was quite long ago, it is at least possible that it was not the recent action (updates) that broke something ... Oct 29, 2015 at 21:10

1 Answer 1


You can uninstall updates from command line with this code:

wusa /uninstall /kb:{update ID}

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