I had the following problem:
I have installed XP sp3
on a PC then I have tried to install linux, I don't know why but LILO and Grub does not worked for me, then I decided to leave XP alone.
When I tried to make a fixmbr from XP CD it hangs at "Setup is inspecting your hardware configuration".
I have tried the next:
-Swap master and slaves
-fdisk /mbr (from old DOS)
nothing worked for me except one thing:
I had to delete the extended partition using fdisk from a DOS floppy,( but only the extended partition ), And make primary partition as "active", then when I restart the PC using XP CD it runs well, then I used recovery function to do a "fixmbr", now XP is running again.
I expect this post to be useful.