Do you have the original case that the disk came in? It's a 3-way folder. On one of the sides is a yellowish-colored sticker with an icon of a key that has the key code. Use this to activate Windows. If you don't have this, look on the side of your case or the manuals that came with your computer. If you don't have one, then buy another copy (a legal copy) though chances are, you can't get XP any more, it's Windows 7.