Moving UserName from one install to anot

I recently put in another motherboard, and my original WinXP refused to boot, fatal errors. Recovery has not worked to date. I reinstalled WinXP along side it, not over it, so as not to disrupt too much data. I need to move my login username fromone install to the other so I can login with my administrators rights under my original username and password. That is still in the original window directory. what and where do I copy to my other install? Then what do a adjust in the registry? Trying to open, copy, or move my “encrypted” files is impossible, actions are denied. Are my “keys” and certificates still in the original windows? Do I need to move them too? Mike