When using an Enterprise connected computer, you receive an activation error code 0xC004F039, it means that the computer is having trouble connecting with the KMS server. The full error message goes like

The Software Protection Service reported that the computer could not be activated. The Key Management Service (KMS) is not enabled.

When the client computer tries to connect with the KMS and doesn't get a response, then its a network issue.

1] Make sure to troubleshoot the network connection between the KMS host and the client.
2] In the KMS firewall settings, make sure that the TCP port 1688 (default) is not blocked by a firewall or otherwise filtered.