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#51
After Updates, computer blues screens with error codes c000021a, - Microsoft Answers
It runs Winlogon.exe or Csrss.exe in usermode. since there is a fatal error it cannot garantuee security, so it swaps to kernel mode. Since winlogin is needed for logon process it crashes.
Did you do a "system restore" to a date prior to possible infection? try an earlier restore point.
and perform a malware check