After changing your computer name in a TCP/IP network, you can still PING your old computer name (and new one). IPCONFIG /ALL returns your old computer name.
By default, the DNS host name is your computer name. When you change your computer name, your host name does not change.
If another computer, using TCP/IP, has your old computer name (or host name), a PING returns the IP address of your computer.
When you PING by name, Windows NT responds with the computer name or host name that matches.
IPCONFIG /ALL only displays the DNS host name.
Use Control Panel / Network / Protocols / TCP/IP / Properties / DNS to change the Host Name to match your new computer name.
Windows NT TCP/IP does not require that your computer name matches your host name.