Windows 7 Boot Error - c000021a
December 24, 2011
So I awoke this Christmas Eve morning to a present from my Windows 7 machine - a Blue Screen of Death (BSOD) with the an error code of c000021a. Doing a bit of research on this error, I found... nothing helpful.
For hours I worked on the issue. I tried everything I could think of:
After all that, I was quite discourage. I hadn't backed up any of my files yet, and I would have liked to back up my files properly. Eventually, I ran across this article, which didn't really have anything to do with my particular error, other than they couldn't get their PC to boot either. I tried performing the answer in the article:
For hours I worked on the issue. I tried everything I could think of:
- Reboot into Safe Mode - Failed. It gave me the same error as if I was trying to boot normally.
- Launch Startup Repair - Startup Repair was able to detect that I was having issues booting, but was unable to fix the issue.
- System Restore - Tried to perform a system restore, but the computer said that before I could restore, I need to turn on System Protection (which was already on, and which I could only get to by booting into Windows - GRRRR!!!!)
- Command Prompt (Disk Checker) - No errors with the hard drive (at least its not a hardware failure)
- Command Prompt (SFC) - I attempted to run the system file checker from the command prompt (through startup repair), but at first it was saying I could not run it because another repair operation was running. I then found that if I ran the following command, it should have worked through startup repair:
SFC /SCANNOW /OFFWINDIR=C:Windows /OFFBOOTDIR=C:
But, that didn't work either. :( - Renamed all AVG Files - I thought (at one point) that AVG might be to blame, because the last couple of files I saw Safe Mode processing were AVG related ones. So, I renamed all related AVG files, and tried that. Nope.
After all that, I was quite discourage. I hadn't backed up any of my files yet, and I would have liked to back up my files properly. Eventually, I ran across this article, which didn't really have anything to do with my particular error, other than they couldn't get their PC to boot either. I tried performing the answer in the article:
Low and behold, this worked! As you may imagine, I was pretty happy :) So now, time to do a proper backup...Answer by Pegasus [MVP] at Microsoft Answers
- Keep tapping F8 during the early boot phase.
- Select Repair from the menu that looks like this one:
http://windows.microsoft.com/en-US/windows-vista/Advanced-startup-options-including-safe-mode- Log on as Administrator if prompted.
- Select Repair when prompted.
- Select the Command Prompt from the menu that looks like this one:
http://windows.microsoft.com/en-US/windows7/What-are-the-system-recovery-options-in-Windows-7- Identify the correct drive letter for your Windows installation. It could be a drive other than C: but it won't be X:. You do it by typing the commands
dir C:Win*
dir D:Win*
dir E:Win*
until you find the Windows folder.
I will call that drive "Q:".- Type these commands:
cd /d Q:windowsSystem32config
xcopy *.* Q:MyRegBack
cd RegBack
dir- Examine the dates of the Software, System and SAM files. Were the files created before or after your problem became apparent?
- If they were made before the problem became apparent then you can type these commands:
copy /y software ..
copy /y System ..
copy /y Sam ..
(the two dots are part of each command)- Reboot normally. If things do not work out then you can backtrack by copying the original registry files from Q:MyRegBack to Q:WindowsSystem32config.