Xp reboot troubles

I have a Toshiba satellite pro 6100 that was running xp pro. One day windows wouldn't load, and i had a technician tell me the hard drive was old and i was sol. (for 220 bucks! ) Later out of curiosity I put in the xp pro os disk from my son's hp..and mine rebooted. Problem is i have to activate the new os, plus I can still see all my old files, but not use any Office programs, etc. I get a little window that says this program is not authorized for current user. I really wish I could have restored with a toshiba disk. Toshiba told me that they were no longer available, but now I see some online. What would happen if i reboot again from a toshiba disk..Will all my files still be there?Can I ever get it back to where it was before? Thanks.