Try Chkdsk /p ,then chkdsk /r after booting to recovery console using the disk.It fixes the in case it doesn't Follow the below
This is what I know abt this issue
CAUSE
The STOP 0xC000021A error occurs when either Winlogon.exe or Csrss.exe fails. When the Windows NT kernel detects that either of these processes has stopped, it stops the system and raises the STOP 0xC000021A error. This error may have several causes. Among them are the following:
•Mismatched system files have been installed.
•A Service Pack installation has failed.
•A backup program that is used to restore a hard disk did not correctly restore files that may have been in use.
•An incompatible third-party program has been installed.
RESOLUTION
To troubleshoot this problem, you must determine which of these processes failed and why.
To determine which process failed, register Dr. Watson as the default system debugger (if it is not already the default debugger). Dr. Watson for Windows NT logs diagnostic information about process failures to a log file (Drwtsn32.log). Also, you can configure this program to produce memory dump files of failed processes that you can analyze in a debugger to determine why a process fails.
To set up Dr. Watson to trap user-mode program errors, follow these steps:
1. At a command prompt, type System Root \System32\Drwtsn32.exe -I , and then press ENTER.
This command configures Dr. Watson as the default system debugger.
2.At a command prompt, type System Root \System32\Drwtsn32.exe , and then select the following options:
Append to existing log file
Create crash dump
Visual Notification
3. After the computer restarts from the STOP 0xC000021A error, run Dr. Watson (Drwtsn32.exe).
4. View the Dr. Watson log to determine what user mode process may be causing the problem.
5. If the Dr. Watson log does not contain sufficient information to determine the cause of the problem, analyze the User.dmp file to determine the cause of the STOP 0xC000021A error.
If Dr. Watson did not create a User.dmp file for either Winlogon.exe or Csrss.exe, you may have to use a different tool to generate a memory dump file of the process that fails.
Note Follow the instructions in the KB articles from MSR to troubleshoot a process that shuts down with an exception. While you follow these instructions, monitor the following processes to troubleshoot the STOP 0xC000021A error:
•Winlogon.exe
•Csrss.exe
Note Most STOP 0xC000021A errors occur because Winlogon.exe fails. This typically occurs because of a faulty third-party Graphical Identification and Authentication (GINA) DLL. The GINA is a replaceable DLL component that Winlogon.exe loads. The GINA implements the authentication policy of the interactive logon model. The GINA performs all identification and authentication user interactions.
It is very common for certain types of remote control software to replace the default Windows GINA DLL (Msgina.dll). Therefore, a good first step is to examine the system to see if it has a third-party GINA DLL. To do this, locate the following registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Value = GinaDLL REG_SZ
•If the Gina DLL value is present and if it is anything other than Msgina.dll, it probably means that a third-party product has changed this value.
•If this value is not present, the system uses Msgina.dll as the default GINA DLL.
Last known good configuration
If the previous steps in this article do not resolve the problem, start the computer by using the last known good configuration. To start the computer by using the last known good configuration, follow these steps: Note Because there are several versions of Microsoft Windows, the following steps may be different on your computer. If they are, see your product documentation to complete these steps. 1. Click Start, and then click Shut Down.
2. Click Restart, and then click OK.
3. Press F8 at the indicated time: • For an x86-based computer: When a screen of text appears and then disappears , press F8. (The screen of text may include a memory test, lines about the BIOS, and other lines.) There may also be a prompt that tells you when to press F8.
• For an Itanium architecture-based computer: After you make your selection from the boot menu, press F8. There may be a prompt that tells you when to press F8.
4. Use the arrow keys to select Last Known Good Configuration, and then press ENTER.
NUM LOCK must be off before the arrow keys on the numeric keypad will function.
5. Use the arrow keys to highlight an operating system, and then press ENTER.
Notes • Choosing the Last Known Good Configuration startup option provides a way to recover from problems such as a newly added driver that may be incorrect for your hardware. However, it does not solve problems that are caused by corrupted or missing drivers or files.
• When you choose the Last Known Good Configuration option, only the information in registry key HKLM\System\CurrentControlSet is restored. Any changes you have made in other registry keys remain.
If all the above do not work u have to do a in place upgrade aka repair installation
