Open Services and restart the LogMeIn Hamachi 2.0 Tunneling service. Then open Network Connections and make sure the Hamachi Virtual Adapter is enabled.
If the problem persists, just download Hamachi again and install again. It should correct any problems regarding the service and adapter.
Sorry I didn't explain anything in depth, if you need instructions, just ask (also tell me what version of Windows you have).
~Cameron