Windows won't boot anymore (c000021a)


A client can't boot Windows 7 anymore

A blue screen rapidly appears and then disappears with the error c000021a (0xc000012f)
Tried a repair; restore isn't an option
I can't execute an in place repair because I can't boot into Windows
I can't run sfc /scannow from the Recovery section of the DVD setup

any ideas on how to get this system up and running again without a Windows reinstall ?

Yann ShukorOwnerAsked:
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JohnBusiness Consultant (Owner)Commented:
That error is quite serious and may be cause by driver updates that have occurred recently.

On a restart, try pressing F8 repeatedly to get into Safe Mode. Can you get into Safe Mode, and if so does it start?

You can try updating all drivers again to see if that works.

Failing the above, you will need to back up and install Windows fresh

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Yann ShukorOwnerAuthor Commented:
Thanks for your reply John
Nope safe mode blue-screens as well

thanks Andre
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JohnBusiness Consultant (Owner)Commented:
You should get the Hardware test application from you computer manufacturer, make a bootable USB for the tools and test hardware.  

Then, if hardware is OK, you need to back up and reinstall Windows.
Can you press F8 to get to advanced boot options so you can diable the automatic restart. That why you can read the full error message.
From the top of my head, that code sometimes appears with a corrupted registry.
If that's so, try get an earlier one from one of the restore points, and replace your current registry (you can use a live windows or linux boot cd/usb for that)
fred hakimRetired ITCommented:
Check your hardware (cpu, disk, memory)  to make sure it passes basic diagnostics.   You don't describe the PC, so its hard to say which self booting tools to use (some boot to DOS, Some Linux, some will not work with UEFI).  Newer PCs pretty much are all setup to boot UEFI.   Some allow you to change that in the bios config, so do not.  

Lazesoft suite has a stable of tools to help repair Windows start up issues.   Download it to a good PC, it will allow you to create a bootable USB or DVD/CD.   The latest version gives an option to create a UEFI bootable or Legacy bootable device -- select wisely.  Then you can try those tools on the failing PC.   It boots into a windows environment, so you have some of those capabilities (like windows explorer) available as well.   It does NOT include hardware diagnostics, but if it boots up, that's an indication CPU and memory might be OK.  

If you create a bootable USB, you can add a few diagnostics on the USB.  Just add a Tools folder to the USB that Lazesoft created, then place any windows portable apps like memtest and cpu stability test or others in that folder.   Later, when booted from the lazesoft disk, you can access those simple tests and run them.


for some portable testing apps.  Note, some have a  64 bit and a 32 bit version and require the matching version for your PC
post the dmp file plse - find it in windows\minidumps
you can access it by hooking the drive to a working pc, or boot from a live cd - like knoppix
Yann ShukorOwnerAuthor Commented:
This client has chosen to have the computer reinstalled without any further investigation of the cause for its breakdown
JohnBusiness Consultant (Owner)Commented:
Thanks for the update
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