I don't understand how I could reboot a server that's offline. I can't access SSH since it won't connect, and I can't access WHM or Virtuozzo or anything like that because it's offline. What would I do...
Sounds like you are on a VPS. If you are unable to access the control panel for the VPS node (which should be a different address than your server), then you need to contact your host to find out why your server is down.