We have a network with various domains.
Under domain A, it is appearing a computer which does not belong to
this domain.
Client is not accessible browsing networkm, but it answers pings.
I see a netbios establish between it and pdc.

I guess that long time ago, this client got admin password and he
joined the domain. It does not belong to a trusting domain,
How can I remove it from the domain?
It does not appear under SERVER MANAGER (grey out).
How can I know which username is using to login under the domain?

Any help will be welcomed.