I am getting this error, what is going on?

This Previously Answered Question may be of help:

https://www.experts-exchange.com/questions/20790028/message-on-bootup-stop-c000021a-fatal-system-error-the-windows-logon-process-system-process-terminated-unexpectedly.html
message on bootup - stop c000021a {fatal system error} the windows logon process system process terminated unexpectedly

If you have Norton GoBack installed: http://service1.symantec.com/SUPPORT/goback.nsf/docid/2003111717232458?OpenDocument&lg=en&ct=aa&seg=hho&src=hot

It can be any number of things...

Need more information - have you installed any new hardware or software?
Have you got up-to-date antivirus and anti-malware software?

Can you interupt the normal boot process, and load into SAFE MODE?

While the machine is first starting to boot up, you can press F8 (usually) repeatedly
until a selection screen appears. You should be able to choose a few safe mode options
from the list. I would probably try "Safe Mode with Networking" so I can do research or
download tools to correct the problem.. If it still fails, try without Networking.

It will not work in safe mode.  I have read through the previous post but nothing makes sense.  This computer is not and has not been connected to the internet.  I tried to re-install windows but still after re-boot same message. No new hardware has been installed, software update for a design program was done over a month ago and system worked fine till now.  
System is:
Dell dimension 4600i, pentium 4 2.66ghz, bios a07, xp pro sp2, 512 mb ddr sdram.

I recently tried to run using "last known good configuration".  Now the error message says:

STOP: c0000221 {bad image checksum} The image url.dll is possibly corrupt.  The header checksum does not match the computed checksum.

Now I'm really ?

Have you recently updated any driver on your Dell machine with drivers other than Dell drivers?

d_may

No, I have not updated any drivers for quite awhile.

I found this web page helped me understand the problem you are having.
http://www.jsifaq.com/SF/Tips/Tip.aspx?id=0907

d_may

Ok, so I ran the Dell symptom tree from the utility partition and ran the tests for "blue screen" and "os will not load".  I got numerous errors that mainly included:

error code - 0f00:0244
message block - 6564084 "uncorrectable data error or media is write protected"

the other errors were the same explanation but with different message block numbers.

Is there a fairly simple way for me to just to erase the hdd and load xp back in?  At this point the info lost is not as important as getting this machine running again.

Well, if you want to do a clean install and forget about recovery of any data, just insert your XP CD and follow the instructions for deleting the partition, re-creating it, formatting it, and setup of XP.  A complete guide to the process, with screen shots, can be found here:

http://www.winsupersite.com/showcase/windowsxp_sg_clean.asp

Thanks d_may,  all went well until I got to screen #8 (copying files portion) I got a message saying that "setup cant copy file" re-try or skip.  I re-tried but eventually had to skip the following files:
mfc40.dll, mfc40u.dll, watchdog.sys, csrsrv.dll

After it copied the remaining files the system re-started and went back to blue screen with my origional error message stop: c000021a {fatal system error} The session manager initializationsystem process terminated unexpectedly with a status of 0xc000026c (0x00000000 0x00000000) The system has been shut down.

So now I am back to square one again, I' have been searching everywhere I can think to find info on this but nothing seems to work.  I would rather keep my data of course but its looking rather bleak.

To help troubleshoot error messages or other issues when you cannot determine the cause of the issue, disable common startup programs, settings, and drivers to eliminate possible software conflicts when you start Microsoft Windows XP. This procedure is known as "clean booting." This article describes how to perform a clean boot, how to start the Windows Installer service, and how to restore your computer from a clean boot state.

http://support.microsoft.com/default.aspx?scid=kb;en-us;310353

d_may

Its impossible for me to do that being that I cannot start windows whatsoever.

Back before I logged into the question, you said this:

>Is there a fairly simple way for me to just to erase the hdd and load xp back in?

And I gave a page giving instructions for doing a clean install.

However, you also said that having run Dell diagnostics, you get the message "uncorrectable data error or media is write protected".  This could be a symptom of a failing harddrive.  Have you tried running "chkdsk c: /r" in the Recovery Console (assuming you have a WinXP bootable install CD)?  This page has some other possible solutions for that problem:

http://hardware.mcse.ms/archive14-2005-1-137177.html

SUCCESS!

I copied the files that the xp repair process from the cd skipped from another computer to a diskette and copied them to the appropriate folder using the recovery console.  Then again I ran the repair process from the cd and boom, bang, cheers.  All files and programs recovered.  Hope this does'nt happen again.  I am not sure who to thank, you all have been alot of help in getting this rectified, although d-may did give me the recovery process.  THanks again.

 Comment from d_may
Date: 01/27/2007 05:39AM PST
      Comment       Accept

Here are step-by-step instructions with abundant screen shots
waiting for you here:
http://www.informationweek.com/windows/showArticle.jhtml?articleID=189400897

With this information, you should almost never have to face a dreaded start-
over, from-scratch reformat/reinstall of XP!

d_may