HELP - XP wont boot

My Pc POSTs, and after the XP WELCOME window I get a blue screen that says "SYSTEM SHUT DOWN -FATAL SYSTEM ERROR THE WINDOW SUBSYSTEM SYSTEM PROCESS TERMINATED UNEXPECTEDLY WITH A SDTATUS OF OX ....."
I have checked evrything That I know how to check - which is not much.
Appreciate your help.

Firstly, take your time to write down the error text EXACTLY, INCLUDING NUMBERS like 0x00000001 and all. This could tell us a lot.

Secondly, describe your system - CPU\Mobo, HDD setup... How much HDD's? Do you have RAID?

Third, what caused this error? Did you change/upgrade something, or it just banged out of nowhere?