My Arduino Duemilanove will not power on via external power supply through the jack. It does however turn on via USB. I also tried hooking up power to the vin and ground power connectors and nothing.
Did I fry my external power situation? I might have accidentally had the jack pluged in and turned on my power supply, and for a second or two it was on 24v. I'm guessing I fried it. How can you check to see?