I had much the same problem with a notebook handed to me to fix; auto-reboot was off, so the 0xc000001d error would appear each time the machine attempted to start (by way of a blue screen).
Initial attempts at a chkdsk failed (no CD drive, had to start it via USB). I made another attempt the next day, so I could Google the error message, but to my surprise it suddenly decided to do the job and repair whatever filesystem errors it was complaining about. Unfortunately this had no effect on the blue screens.
Following the information posted above, I replaced csrss.exe, win32k.sys and winlogon.exe from a machine running XP SP2. This got me to the login screen, but after entering the password, Explorer promptly crashed. Task Manager worked and I had Command Prompt access.
I checked regional settings, but the computer seemed to be set to defaults in that area - see http://support.microsoft.com/kb/192806 as to how to get into control panel areas with only a command prompt.
The solution from there was easy in my case: Open a prompt window, rename c:\windows\explorer.exe, then replace it with a copy from the SP2 rig. On renaming the original, Windows promptly started complaining about system files being missing, and prompted me to insert an SP3 disc to replace them; though it shut up after I put the copy from the other computer in place and rebooted.
I'm getting security warnings when trying to copy files at times, which probably has to do with the mismatched system file versions. Presumably all would be fine if I'd had access to an SP3 disc, though these are the sort of errors that go away just by clicking an "ok" button.
The proper way to go about things is probably with the System File Checker (SFC), though I dunno if that'll run from the recovery console. This tool does require access to a disc to work properly though.
http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/system_file_checker.mspx?mfr=true
After a few error messages (btTool.exe) my pc got a BSOD and rebooted. The pc was unable to boot and kept throwing a BSOD: CRITICAL SERVICE FAILURE. The only way I could boot Windows was by booting with the option "Disable driver signature enforcement".
I tried a lot of things: memory tests, sfc, bcdedit options, ... . Unfortunately without luck.
I fixed this issue by doing a repair using a Windows 10 .iso and just doing an installation of Windows overriding the current version with keeping files and apps. This repair took two hours and the system is working and booting fine now.
Best Answer
Stop C000021a is fatal system error that occurs early in the boot process during initialization with the Session Manager. The status code 0xc000003a indicates STATUS_OBJECT_PATH_NOT_FOUND. You may work around the issue by disabling integrity checks or by permitting test signing on drivers on boot.
The issue is evidently being caused by a device driver that is corrupt or not properly signed. Disabling Driver Signature is of course not an acceptable workaround.
I will describe below a procedure for testing where is the error and of fixing it. If when following it you encounter any error condition, report it in your post and do not continue.
Step 1 : Corruption checks
To check for corruption execute the following :
S.M.A.R.T. test to check for general disk failure using a utility such as Speccy. For interpreting the results where unclear refer to this answer.
Run the command
chkdsk C:
. For more information see this article, but in case of error, report to us and do not execute yet any of the repair options.Run
sfc /scannow
to check Windows integrity as described in this article.If all tests have passed, continue on.
Step 2 : Locate bad driver
List the drivers as they are being loaded during the boot process in an effort to determine which driver may be causing the crash, returning driver checks, by running in an elevated Command Prompt (cmd) the commands:
Reboot and tell us the name of the last driver to be displayed. If the name disappears too fast when the crash occurs, film the boot process using your telephone.
Let us know which driver it is before continuing.
Once the bad driver is identified, you may :
Uninstall device
If the above has not helped, continue on.
Step 3 : Take backups
Disable again Driver Signature Verification and boot to save all your files.
I also suggest that you take as backup an image of the system disk on some external disk. My favorite product is AOMEI Backupper freeware. If you use AOMEI, create an AOMEI Bootable Disc or USB as described here, boot it and verify that it can see your backup, just in case.
Step 4 : Repair Windows
Disable again Driver Signature Verification and boot into Windows. Do a Repair Install from your boot media as described here. It is important to use a boot media that corresponds to your service-pack level (SP1?). This will conserve your applications and drivers and most system settings.
If Windows can then boot with Driver Signature Verification enabled, then all is fine. Execute Windows Update repeatedly until all updates are done.
Otherwise, you are in trouble and need to reinstall Windows from scratch.