XP error messages

Every time i log on to Windws Xp an error message appears that reads" winlogon.exe failed". A blue screen appears after that reads " c000021a {Fatal System Error}. After that my computer is frozen and i have to restart it. I have tried doing system restore in safe mode on 2 seperate dates but it will not let me go back to that date. Any suggestions would be really appreciated. Thanks

 

Try a repair installation:

How to Repair Install:
Note: You will need to reinstall SP2 and any Critical Updates from the Windows Update Site after the repair.

There are two approaches. The first one should be used if you can still boot to your Windows Desktop. Simply pop the XP CD into the CD-Rom drive and select Install->Upgrade[recommended]. This will install XP overtop of itself in the same way as upgrading from a previous setup. However if your version is an OEM version then you will not have this option. If you do not see the option to Upgrade[recommended] DO NOT choose New Install as that will either overwrite your current setup completely or give you a dual boot setup. Also if you have an older version of XP and have upgraded to a new service pack you will get a message stating that a newer version of Windows was found and you will not be able to run the Upgrade.

If you cannot boot to the Desktop, or you have an OEM version of XP, or you want to remove a service pack then the following should be used to complete a Repair Install:
Boot with the Windows XP CD and at the Setup Screen press the Enter Key
You will be taken to the Windows XP Licensing Agreement. After reading the agreement press F8 to proceed.
The next screen gives you the option to do a fresh (clean) install or to repair the selected Windows XP installation. To run a Repair Install Press "R" at this time.
***CAUTION*** if you do not see the option to repair the selected Windows XP installation DO NOT choose the option to continue installing a fresh copy without repairing as that will overwrite your data and cause unrecoverable data loss.
Windows XP will copy the necessary files to your Hard Drive to begin the installation and will then reboot. You will see the message that informs you to "Press any key to boot the CD". Do not press any keys this time just wait a few seconds and the Windows Startup Screen will be displayed. Following this you will be greeted by the Windows XP Setup Screens.
When Setup has completed you should find all of your previously installed apps and settings are intact.

 

Hi!
This info may help:
http://support.microsoft.com/kb/156669/?sd=RMVP#appliesto
How to troubleshoot a "STOP 0xC000021A" error

and this if you have Go Back:
GoBack Causes a Stop Error C000021a
http://support.microsoft.com/?kbid=316503&sd=RMVP#appliesto

 

>> Every time i log on to Windws Xp an error message appears that reads" winlogon.exe failed". A blue screen appears after that reads " c000021a {Fatal System Error}. <<

Check out the following webpage link:
Microsoft Knowledgebase Article ID: 156669
How to troubleshoot a "STOP 0xC000021A" error​

Good Luck!