I am very very far, from being a "genius", but I do know one thing for sure>>>
To get your computer back to looking like new, do "a system recovery"
I do not have the disk either. My windows XP, was already loaded on my computer, when I bought it. These instructions, will clean everything off of your hard drive, so you must back up anything that you want to save. I have done this three times, and I got these instructions, from a computer tech. When starting your computer, tap the F-10 key. click on next-yes-and follow the instructions, that come up on your screen. When you are finished, your computer, will look just like it did, when you first bought it.Do these steps, in order, when finished.
1. set up windows firewall, in control panel
2. windows update (click express)
3. install your anti-virus program (update)
4. install anti-spyware (update)
Or you can use this program, to get your key number>>
http://www.magicaljellybean.com/keyfinder.shtml