Windows 8 Pro cannot boot - Error 0xC000021a

Hi Jennie. I couldn't boot either. I had given up. Until Windows 10 came alone with their free upgrade. It made it possible to make an ISO file and burn it to disk on another computer. Go to - http://www.microsoft.com/en-us/software-download/windows10. If you can boot, you can upgrade directly. If not, their is a media tool to download the ISO file that you can burn to a DVD. That will install on your computer with the broken windows 8. It will ask for a Key that you will not have. It will also offer a option to skip this step. (Not forever, just to get the install completed.) Once it is installed it will work as an unregistered copy. But in recovery, their will be a back out. Allowing you to revert to your previous version. This might just fix the boot record in the restore process. Once you can boot in the recovered win 8. You can upgrade to win 10 from the same link. Also for anyone who does have a win 8 key. you can download the iso from http://www.microsoft.com/en-us/software-download/windows8 .

Interesting that this thread has been running for nearly 3 years and there continues to be problems...In case anyone at Microsoft was wondering why people generally dislike Windows 8?

Similar to everyone else, but I hit the same error code on a clean install of the 64-bit Pro version.  This is in the initial UEFI boot before the program is installed on the HDD, so can't even get to safe mode or repair console.  Have read up all over the internet and tried numerous solutions but to no avail.  Previously installed Windows XP on my new build (my Windows 8 is an upgrade) and it installed without a hitch.  Ran the upgrade (not update) from Windows XP to Windows 8 and same problem - Seemed to install fine until the first reboot and then got stuck in the error cycle.  Switch off, restart and same error.  All I want is to get my Windows 10 going (which I already have downloaded and ready to go) and here I am stuck trying to make Windows 8 work to get to the end goal!

Microsoft you are making your customers spend thousands of valuable hours installing error ridden OSs to be able to upgrade to the better(?) Windows 10.  Is there really not another solution you can offer?

A bit late in the day I know but the error was caused by a security update called KB2823324.

Microsoft released a support article recommending users remove it and the article contains various methods of achieving that goal: https://support.microsoft.com/en-gb/kb/2839011

The update was subsequently removed from Windows Update and replaced by this one: https://support.microsoft.com/en-gb/kb/2840149

I hope my contribution here at least goes some way to explain why it occurred.

As regards Windows 10, users should be aware that all updates are mandatory and will take place regardless of whether a user agrees with them or not. So I think it's only a matter of time before history repeats itself.

Hi

I have got similar problem with my Windows 8 Pro  PC. It worked, after 2 years of using win 8 I saw error code 0xc000021a. Then, it showed me: shut down and somerhing like advanced options. I choosed advanced options.

Safe mode boot doesnt worked. In cmd i tried chkdsk c: /r . I dont know why, it was only idea. Nothing changed... At last I tried the easiest thing. I click on Troubleshoot-> Advanced options-> System restore

Computer worked right.

How do you do that?