0xc000021a after Windows Updates

If, after you apply Windows Updates and reboot your computer, you get a blue screen with code 0xc000021a here are a couple of things that you can try:

Corrupt Driver Signature Catalog Files

1. When the systems boots up, press F8 repeatedly until you get the Advanced Boot Option Screen
2. Choose the option "Disable Driver Signature Enforcement"
3. If the system boots up then you most likely have corrupt driver signature catalog files. To check which drivers are not signed you can use sigverif

Corrupt Registry Entries

1. When the systems boots up, press F8 repeatedly until you get the Advanced Boot Option Screen (or boot with a Windows DVD)
2. Choose the Repair Your Computer option
3. Open Command Prompt
4. Replace the SYSTEM and SOFTWARE registry hives by running the following commands (assuming OsDrive as C: below but it may differ on your system):
   1. cd C:WindowsSystem32config
   2. ren SYSTEM SYSTEM.old
   3. ren SOFTWARE SOFTWARE.old
   4. copy C:WindowsSystem32configRegBackSYSTEM C:WindowsSystem32config
   5. copy C:WindowsSystem32configRegBackSOFTWARE C:WindowsSystem32config
5. Reboot system