Many don't have the real RETAIL XP SP2 CD so my advice will sound foreign and can't be used.
I just fixed a non-booter with the XP SP2 CD and the FIXMBR and FIXBOOT commands. Did you try those?
One day recently, my computer refused to boot up. It got one step after the BIOS info and ?drives detected?, then froze with a completely black screen. Although the drive had become non-bootable, it could still be read if I booted from another source!
I tried all I could think of, including trying to repair the Windows system by booting from my original Windows XP disk. Even doing that, the computer still froze in the same manner.
I installed another disk, but could not restore a ghost image of the old drive (which made me a bit miffed!) I've had to install Windows XP again, and had all the pain and hassle of re-installing all my other software.
Anyway, anyone got any ideas on the original (non-booting) problem?