This generally occurs when xp has not been activated within the 15 day period from install.
You can try a reinstall of the OS or try this
Copy the file c:\windows\system32\wpa.dbl to a floppy.
Reinstall Windows XP.
Boot to a DOS disk if you are using FAT, or to the Recovery Console if using NTFS.
Copy the file from the first step above back to c:\windows\system32.