Our 5 year old laptop, on XP, has been playing up a bit recently.
Now it has a message:
Windows could not start because the following file is missing or corrupt
\WINDOWS\SYSTEM32\CONFIG\SYSTEM
It then asks for the original set up discs, but we didn't get any with the computer. (I now hear I should have made some 'recovery discs', but I didn't know that before)
Have you tried holding down F8 during the boot process? If it works, it will take you into Safe Mode, from where you can access System Restore. (Start > Programs > Accessories > System Tools > System Restore).