I rebooted xp on my old toshiba from an xp disk from an hp

My pre-onwed (with no recovery disk)toshiba satellite pro 6100 got hot and crashed windows. I paid a guy 220 bucks to say the hdd was probably bad. and he left me sol. I decided to try and reboot using my son's hp os disk. It worked. hdd must be ok? Anyway, now windows needs a new activation key, also i am able see all my old files by going to c drive/program files...but can't use any of my office programs..doesnt authorize current user.