Same here. I had to format a week ago and installed a legal copy of Windows XP.
I was able to commence the installation using the Product ID on my Certificate Of Authenticity (stuck on the PC), but when it came to activating it, it said that my Product ID was not valid, not found in the database.
Had to activate using the telephone, but automation said it was invalid too. Then a support rep. finally managed to verify that my OS was genuine (after telling him my version of Windows XP was a Pre-Installed OEM copy from HP).
But then a week later, I get a message in XP saying 'Hardware had changed significantly over the past 3 days and you will need to re-activate Windows XP'...!!!
. Then when I tried activating by typing my Product ID again, it said I had exceeded the limit which I can attempt to use the key.
Telephoned yet again, automation said it was invalid, and same happened...support rep. only managed to validate my copy when I told her that it was a Pre-Installed OEM version.
...A problem there.