win 2000 Laptop can’t release IP address

I have a win 2000 Pro laptop in a school network that doesn’t release the old IP address. This laptop was getting Ip address from a DHCP server. Lately the address it was using was reserved for some other use. It’s giving “IP address conflict”
error message and can’t logon to the domain everytime it reboots. I’ve tried using dos command “IPconfig/release” & “IPconfig/release/all” and it still will not release. I’ve tried uninstall TCP/IP and reinstall it, problem still there. I gave it a static IP but it still have the error message. What else can I try ? Can I force release it in the registry ? Please show step by step. Thanks.