My Arduino Duemilanove wont power on?

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?

I think you have fried the 5V stabilizer MC33269D-5. It can withstand max. 20V and you have used 24V - 0.7V (for a diode onboard) = 23.3V.

Make a test: Supply the board via the black power supply jack with about 9V or 12V. Centre pin = +. Measure the input voltage at pin 3 and the output voltage at pin 2 of this stabilizer. It is soldered just above the power supply jack. Here is the datasheet to find the pins: http://www.alldatasheet.net/datasheet-pdf/pdf/12030/ONSEMI/MC33269D.html

Pin 2 is also connected with its heatsink. If you can not see 5V, it is damaged.

Got 12v running to the power jack center +. measured the input voltage at pin 3 and the output voltage at pin 2 of the stabalizer. I have 5.2 volts! What else could it be?

That's really strange. On the other hand the 5.2V is a bit too high. The maximal output should be 5.05V. Maybe it's due to the imperfection of your voltmeter. Or due to the waveform of the power supply. Is it a switched mode one? Can you check the board by another source?