MIDI i/o with arduino NOT connected to computer???

I am fairly new programing the arduino so I would greatly appreciate any help you can give!

I am able to get the code and hardware to work great as posted by kuk on the following popular post = http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1187962258/0 (thank you kuk!).

But I can only get it to work when the arduino is hooked to the computer via the USB cable. I want to be able to load a program onto the arduino that can take in MIDI data and respond as I please without the arduino hooked to a computer. For example, I want to hook my MIDI keyboard up to the arduino, play a note, and in turn an LED on one of the digital pins of the arduino lights up (depending on what note I play).

So, can the arduino take in MIDI data and respond without being hooked to a computer? If so, how is the code written?

Thank you SO much for your help! I am working on a project that would greatly benefit from this!

How does your board get power when it is not plugged into USB?

I use an external power supply ( http://www.radioshack.com/product/index.jsp?productId=2552560 )

Just to be completely clear I am doing everything correctly and it is just code that is the problem = I disconnect the USB and everything else connected to the arduino (so that when I turn on the arduino the bootloader does not listen to the RX pin thinking a program is being loaded on it), plug in the wall-wart and change the jumper on the arduino to external power, put the LED back in pin 13 and ground, press the reset button, let the program load (which it apparently does not completely do as the indicator LED in pin 13 does not turn on as it does when it is plugged into the computer using USB), then plug all the inputs and outputs back on the arduino (put the MIDI input in the RX pin, the MIDI output in the TX pin, plug in the ground and 5V from the arduino to the breadboard I am using for the components for MIDI i/o, plug in LEDs with 220ohm resistors into digital pins and ground). Then I play a note on the MIDI keyboard and no LEDs light up corresponding to the MIDI note I played.

It all worked perfectly when I had the USB plugged into the arduino rather than an external power supply. I think something in the code relies on the computer. I just do not understand what it is.

Thank you for your help!!!