PCs get IP setting from not exist DHCP server

i have replace a server was doing(domain controller, DNS and DHCP) with new server. so all the roles have been replaced to new server and the old server has been killed. but now i have faced a strange problem. some PCs get the old IP settings (old DNS IP address), although the old DHCP server is killed and not exist and they are configured in automatic IP address.

can anybody explain to me, how and from where they get these settings.

many thanks
Walid