how can i find some one computer user name and password by ip address
You are not going to find your answer here. I don't think hacking is supported on this forum.
It's not as if there is an answer. You can't get a username and password just from an IP address. You need to talk to the person who owns the computer and ask them if they are willing to provide that information. If not - well, you would be committing a criminal offence. I'm sure you don't want to do that.