Arduino NG USB board does not run on ext. power

I downloaded the simple blinking light program to the Arduino NG board via the USB connection. It ran as expected. I want to run the board from ext. power, so I disconnected the usb cable, switched the power jumper and connected a 12 VDC wall wart power source. The PWR light cam on as expected but the light did not blink. Is there some inteaction with the USB chip and atmel 168 that keeps a program from running? Anyone else have this difficulty?

You may need to tie the RX pin of the Arduino board to ground with a 10K resistor. Otherwise, the floating pin might mean that garbage data gets read by the bootloader, so it never times out and starts your program. I'll add this to the documentation.

atmel 168

Do you mean the ATMega8, or did you swap in a 168?

My board came with an atmega168. Sorry about the mispelling 'atmel'. Great board!

Tying the Rx pin (digital line 0) to ground via a 10K resister did the trick. Thanks for the help. Guess the floating line caused the UART to hang waiting for a sync state...