Stop code 0xc000021a on a Dell Inspiron

Hi Andy. I'm Greg, awarded MVP for eleven years, Volunteer Moderator, and Independent Advisor here to help you until this is resolved.

Unplug power and remove battery, press and hold power button for 30 seconds to release all power from circuitry, plug back in and power up to see if any change.

I will give you steps and tools needed to access the Repair Mode to try all repairs to get Windows started, and if not to do the automated Reset or the superior Clean Install after rescuing your files. I will be standing by to help as needed and will not let you fail.

1. Use whichever method works in this link to access Advanced Startup Options: https://www.tenforums.com/tutorials/2294-advanc.... Easiest may be to force shut down the PC (by holding in the power button) three separate times to trigger the Startup Options. If one of these methods work, then go to Step 3.
2. If none of the other methods work it may be necessary to Create Windows 10 Installation Media on another PC following the steps in the middle of the downloads page here: http://windows.microsoft.com/en-us/windows-10/m... Make sure to uncheck the box for Recommended Settings to choose only the licensed version.

Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key: https://www.sysnative.com/forums/hardware-tutor...

Choose the boot device as a UEFI device if offered, then on second screen choose Repair Your Computer. If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first. There is always a way to get the media booted and I will guide you until it does, even if necessary to reset the BIOS to defaults via several methods.

3. In the Advanced Troubleshooting options try to System Restore to a point before the problems began, try the new Uninstall Updates button, then Startup Repair, then if necessary from Startup Settings try to get into Safe Mode with Networking, or lastly Safe Mode.

If Startup Settings aren't available you can force Safe Mode from the Command Prompt following Step 5 here: https://www.digitalcitizen.life/4-ways-boot-saf..., or using the command to unhide F8 Advanced Boot Options here: https://www.tenforums.com/tutorials/22455-enabl... where you can also try the old reliable Last Known Good Configuration.

4. From Safe Mode w/Networking work through the Windows 10 Install Integrity Checklist to make sure the install is set up correctly, optimized for best performance, and any needed repairs get done: http://answers.microsoft.com/en-us/windows/wiki....

More on how to diagnose in Safe Mode:

https://www.pcmag.com/news/354269/how-to-use-sa...

Update your drivers from the Dell Support Downloads web page for your Service Tag number on sticker on PC. Compare the latest drivers with the ones presently installed in Device Manager reached by right clicking the Start Menu. Make sure you have the latest BIOS, Chipset, Display (Video), Sound, USB3, Bluetooth, Network and all other drivers, or else download and install the latest now.

5. If Safe Mode doesn’t work or help stabilize things then return to Advanced Troubleshoot options. Next try Command Prompt to run System File Checker to find and fix broken system files: https://www.wintips.org/how-to-run-sfc-offline-..., a full Disk Check: https://www.groovypost.com/howto/check-hard-dri..., run the Bootrec and BCD repair commands as well as other fixes from Troubleshooting Windows 10 Failure to Start: http://answers.microsoft.com/en-us/windows/wiki...
6. If none of the repairs work return to Troubleshoot options to Reset Your Windows 10 PC.
7. Better yet use the same booted media to do the vastly superior Clean Install following the gold standard Clean Install in this link which compiles the best possible Install of Windows which will stay that way as long as you stick with the tools and methods given, has zero reported problems, and is better than any amount of money could buy: http://answers.microsoft.com/en-us/windows/wiki...
8. There is a step to Rescue Files from the booted media or Repair Mode Command Prompt first: http://answers.microsoft.com/en-us/windows/wiki...
9. To test hardware, Dell and HP have onboard diagnostics triggered by powering up and pressing the F12 and ESC key respectively.
10. Test the RAM overnight to stress it with the best bootable test memtest86, following these steps which test both the sticks and the slots:

https://www.wikihow.com/Test-PC-RAM-with-MemTest86

11. Test the hard drive with diagnostics:

https://www.lifewire.com/free-hard-drive-testin...

Best is to use the manufacturer's own if there is one, otherwise use Seatools bootable long test: http://blog.nowherelan.com/2013/04/04/boot-seat...

12. Follow this up with a full Disk Check: https://www.groovypost.com/howto/check-hard-dri...
13. If it doesn't pass both tests then replace the hard drive with an SSD which is the best upgrade you can give the PC, better than a new higher end PC without one, especially if you do the Clean Install from Step 6. It's easy to find a video online that shows how to swap in the SSD for your model PC.
14. Stress test the rest of the hardware:

https://techguided.com/best-tools-to-stress-tes...

https://www.tomshardware.com/reviews/how-to-str...

https://appuals.com/how-to-run-a-cpu-stress-tes...

I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.

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Hi Greg, I realised I hadn't replied to you, I'm sorry. Thank you for your very detailed and helpful reply! With your help I managed to get to Repair Mode, but Windows 10 had completely failed and needed to be reinstalled. That was beyond my abilities so I took it to a local shop and they fixed it. My family who are Mac users are feeling smug. Thanks again for your help. Andy