registering?

[sonic]

i tried to update my xp coz i reformatted my hd recently
and it an error says that there is a problem with my
serial number. that happend when i was installing the
upadate. downloading it was no problem. do i have to
register my number again and how do i do that?

 

[Taurarian]

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q326904
Error Message: The Product Key Used to Install Windows Is Invalid

Is the above related to your problem, you didn't say which update?