Don't forget to mention that you're on "nilla." There's nothing in DreamHostStatus about any recent problems with it.
Most people have only had slowdown or dead sites in the dark days of Dreamhost's network problems, but not lately.
Have you contacted support about this? In the mean time, the server is pingable, so it's not dead. If you can SSH in and look at the Load Average, that might shed some light on the situation.