Same problem here with Kubuntu 10.04. The computer was in standby. It didn't resume from it, instead black screen was shown. Then I forced reboot and since then KNetworkManager showed Unmanaged/Network Management disabled. After changing /var/lib/NetworkManager/NetworkManager.state contents this works again. As already written, KNetworkManager applet should have a checkbox -> enable networking.
Same problem here with Kubuntu 10.04. The computer was in standby. It didn't resume from it, instead black screen was shown. Then I forced reboot and since then KNetworkManager showed Unmanaged/Network Management disabled. After changing /var/lib/ NetworkManager/ NetworkManager. state contents this works again. As already written, KNetworkManager applet should have a checkbox -> enable networking.