windows xp pro uninstall/reinstall

Ok,

So I just found out recently that I'm unable to do any windows updates b/c my key codes do not match. I have another copy of xp pro and I want to install it. I've never taken on a task like this before so my question is how exactly do I go about uninstalling the version I have for another one? Also, are my files going to be safe or will I lose anything if I go through this process? thanks in advance.......

 

Why don't you try to change your product key with something like ROCKXP?