Topic: Server was working, but now: Service Temporarily Unavailable

I had an app running on a server I setup following a deprec tutorial (the peepcode one). Everything was running fine for a couple of weeks, but two nights ago I shut down the system due to bad storms. Now, when I try to access the site I get this page/error:

Service Temporarily Unavailable

The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

When I try accessing localhost from the server itself I get the same page, so I don't think it's a router problem.

I don't think this was the first time that I had reboot the system in the past couple of weeks, so it all seems a bit odd. I'm not ever sure where to begin to diagnose the problem. Any suggestions?