After leaving the domain you can no longer use your domain credentials, simple as that. Your computer will not try to authenticate with a domain controller, so you are forced to log in with a local user account.
I don't know what you mean by "lan network has changed" but if your computer is on a different physical network, that is an additional problem. You cannot contact the proper domain controller on a different LAN (unless you have VPN or similar), and your cached credentials won't work any more anyways.
You're best off going back to the old network and rejoining the domain. If this is not your machine, give it to someone in your IT department and tell them what happened. You shouldn't have been able to leave the domain without supplying domain admin credentials though...