If its a complete reformat, then a reminder or screen for registering the product should appear. Fill in the details and then register. The product details should be on a sticker fixed to the computer. If you do not have a sticker, then the details might be made available by using SIW or JellyBean, both of which are downloadable from the internet.
I am not sure what you mean by 2 Windows XP options. Can you explain further?.
With regards to the blue screen, is this asking for administrator login details?.