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Windows 7: BSOD on boot from clean install bug code 0xc000021a

21 Jun 2015   #1

Widows 7 professional 64 bit
BSOD on boot from clean install bug code 0xc000021a

I recently bought a refurbished thinkpad (T420 i5 2540, SSD, 8gb ram, NVidia nvs 4200) with windows 7 professional. It worked fine at first, I could turn it on without a problem. However, as soon as windows updates installed, and I rebooted it, it refused to turn on. The power and Bluetooth lights would come on, then shut off after a few seconds. I unplugged, removed the battery, and pressed the power button a few times then held it, but that didn't help. After several attempts it finally boots, but BSODs as soon as it gets to "windows is starting". If I leave it for a long time (several hours) and try again, it often starts up normally. This whole process has happened many, many times over the last 3 days, with little difference each time. Launching startup repair just BSODs and it goes back to not turning on at all. System restore doesn't work, and I tried formatting the hard drive and going for a fresh install. It booted normally at first, but as soon as windows updates kicked in, it started failing to boot again. I was able to get a single crash dump (which should be attached). The bug check was 0xc000021a, on ntoskrnl.exe, at address ntoskrnl+72a40. I've tested SSD, ram, processor, etc., but they don't have any issues. I've never really had to deal with repeated BSODs before, so I have no idea what's going on.

TLDR: computer won't boot after windows updates apply, (even on a second, clean install) instead it usually BSODs (though it will occasionally boot correctly). System restore, safe mode, startup repair all fail or just don't fix the problem. If it boots, there are no problems afterward. Bug code from BSOD dump was 0xc000021a.

Thanks for your help

My System SpecsSystem Spec
21 Jun 2015   #2

Microsoft Community Contributor Award Recipient

Microsoft Windows 10 Pro Insider Preview 64-bit

In this case, it would be the best to go for another clean reinstall.

Because, from the description it appears to be a driver issue, a driver is conflicting during startup; and at the time the BSOD occurs, it does not have sufficient information to record the failing module in the dump.

Perform a clean reinstall exactly as suggested here: Clean Reinstall - Factory OEM Windows 7 .... hopefully it will solve this issue.
BugCheck C000021A, {fffff8a001a1dce0, c0000189, 0, 0}

----- ETW minidump data unavailable-----
Probably caused by : ntkrnlmp.exe ( nt!ExpSystemErrorHandler2+5e1 )

Followup: MachineOwner
My System SpecsSystem Spec
21 Jun 2015   #3

Widows 7 professional 64 bit

I may have actually fixed it already. I've rebooted twice with no problem now. It may have either been that everything just needed to finish installing in some invisible background process, or (more likely) that when I used sfc scannow.

If someone else who finds this thread has the same issue, and can get it to turn on, try going to command prompt, (run as administrator) and type "sfc /scannow" (no quotes). You should also be able to boot from recovery, and run it in command prompt there.
My System SpecsSystem Spec


 BSOD on boot from clean install bug code 0xc000021a

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