OK...in order to run fixmbr or fixboot, you need to download the Recovery Console .iso file via the following link: Download Recovery Console, Bootable ISO - http://www.webtree.ca/windowsxp/repair_xp.htm
The file you download will be in .iso format and will need to be transformed to a bootable CD.
This is done by using an .iso-burning program, the one I use is Active@ ISO Burner - http://www.ntfs.com/iso_burner_free.htm
Once you burn the .iso to a CD, it will be bootable. Change the 1st boot option in the BIOS...save the changes and insert the CD before your system starts to boot again. Once the system boots to the CD, you will have access to the Recovery Console.
Once in the RC, your XP install will be reflected as 1 when it lists installs noted. Type 1 on the 1st prompt for whichever XP install you intend to repair...then just hit Enter when prompted for password. On the next prompt, type fixmbr, hit Enter. If you get a warning about non-standard MBR, ignore it.
To run the fixboot command, you can just run that after the fixmbr command completes. Or you can see if the fixmbr command provided any relief by typing Exit and the system will reboot. You can remove the CD before it reboots, you can change the BIOS boot prompt if you so desire...or you can wait to see if the effort was efffective and your system now boots into XP properly.