|You should never have used the disk sanitizer. It is totally unnecessary. Disk sanitizers are designed to clear a hard disk of everything prior to disposal. Depending on which one you used they can even render the disk unusable.|
By using the disk sanitizer you probably erased a hidden partition the is used to reinstall Windows with the OEM disk that came with the computer. In that case you are going to have to contact HP and see what they can do for you.
Otherwise you are going to need to get a full version of Windows XP and install that. That is assuming the hard disk is still usable.