I think that it means that the service has crashed. Something might be interfering with it. Try uninstalling any antivirus program and reinstalling Hamachi. If it works, find another antivirus program.
Wouldn't disabling or even closing the anti-virus be the same? I've already tried that. I am currently paying for Kaspersky, and I'm not sure if I'm willing to give it up since I've had no virus/malware problems ever since I got it.