XP Professional Blue screen

Hi,

I am getting a blue screen with the following message as soon i start up my laptop.

" STOP : c000021a (Fatal System Error)
The windows Logon process system process terminated unexpectedly with a status of 0xc0000005 (0x00000000 0x00000000)
The system has been shut down"

I have Windows XP Professional SP2 on my laptop. I have turned off automatic windows updates as this happened to me last year and that time i had to install the OS fresh. Somewhere i got the recommendation to turn off the automatic updates as some hot fixes gets installed and cause this error. This time on i want to detect the error and fix it without installing the OS.

I looked up microsoft site but it talks about Windows2000 platform.

Any help on this will be appreciated.

Thanks in advance
Abhijit