The nexus is now a service on the server. Sometimes I see the server restart due to an issue via the hosters, and since nexus isn't a service, it never gets added back.
Don't know why the restarts sometimes, this was a similar issue, Everything should be okay within a hour or two and there shouldn't be anymore issues where the NEXUS is down, unless the server is getting ddosed to hell

To mobious: Nexus.exe (Still java never fear, its just a converted bat file for service running) now

If you need to debug or test the nexus let me know and ill shut down the service and let you run it on the SF account.