Windows problems

Question

hello
windows xp shows me a message every time i open my laptop, saying that my windows it is not a valid one. following their advice and the link offered by them and writting the key product on a page(and it didn't match theirs) , i found out that my windows has been blocked because it seems that my laptop is a stoled one.
What can i do?
My laptop is working very very very slow.
thank you