UPGRADE WINDOWS XP MEDIA TO XP PRO

I JUST BOUGHT THE XP PRO UPDATE CD FROM OFFICE DEPOT.
I INSTALL THE CD, CHOOSE TO UPDATE “RECOMENDED”, TYPE IN THE KEY, AND I GET AN ERROR SAYING “THE CD KEY WICH YOU ENTERED IN IS INVALID. PLEASE TRY AGAIN”
I HAVE TRIED NUMERIOUS TIMES WITH CAPPS ON AND OFF, USING THE NUMBER BOARD AND NOT, SAYING NICE WORDS AND NOT….:) I HAVE ALSO TURNED OFF THE ANTIVIRUS…NO GOOD. DOES ANYONE HAVE ANY SUGESTIONS? TRIED TO CONTACT MICROSOFT, CANT GET THROUGH..
THANKS ALL!!!