Because it might be helpful I'm sharing this info with other users.
My old HP notebook refused to boot XP Professional with the referred message. I don't have the administrator password or recovery CDs. I just wanted to save my PC environment and a clean install was not an option.
So, here's how I recovered my XP.
1 - My first objective was to crack the \windows\system32\config\SAM file to get the administrator password (which in the end I didn't need!)
2 - I followed the instructions Creat a bootable USB Ophcrack in Windows USB Pen Drive Linux. Using a working PC I did the two downloads -Universal-USB-Installer-126.96.36.199 and OPHcrack liveCD for XP (had to do disable the PC Anti-Virus - false positives). Run the Installer and choose OPHcrack (just follow the menu options) using the formatted USB pen drive. No problems at all. Removed the USB pen.
2 - After that I inserted the just created bootable USB pen drive in the HP notebook (powered off) - The HP notebook option to boot from USB pen drive won't be available if the pen isn't inserted before power on.
3 - Press Power on and then F9 to allow me to choose boot from USB drive (option is now visible)
4 - Notebook booted from the USB drive. This was the linux SliTaz environment (didn't know it at all)
At this point I've changed my mind and decided to end the process of cracking SAM. Closed the SAKURA window and navigated through the main menu options and soon discovered the SliTaz file manager
This file manager is similar to the windows file Explorer. I've opened it.
1- Select the hard disk clicking on the HDD icon
2- Go to \windows\system32\config\
3- The file SYSTEM is there. I renamed it to OLD_SYSTEM (use the mouse right button)
4- Go to \windows\repair. There's another SYSTEM file there. Copy it (use the mouse right button)
5- Go back to \windows\system32\config\ and paste it
I've exit SliTaz and removed the USB drive.
Power off and on.
XP booted again. Some display resolution configuration was needed. I guess that other devices configurations might need some kind of resetting.
The fact there was a usable SYSTEM file in the repair folder was unknown to me and I don't know if this is replicated in every XP installation.
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