When Houdini licenses are installed directly to the computer, the computer name and hardware information is encoded into the keystring.

If you change the machine name, the Houdini licenses will be no longer work.

Rename your computer back to the original name associated with the licenses and reboot.
If you don't remember the machine name, log into your SideFX account.

The licenses should be recognized once more.

If you want to change the machine name, please refer to the following FAQ to move licenses to a new machine:
www.sidefx.com/faq/question/how-do-i-move-licenses-to-a-different-license-server/

Moving licenses to a new machine name is the same as moving licenses to a new computer.