Power source making a difference?

I have an Arduino Duemilanove, and my program is 100% working and running great when being powered through USB, however, when I switch over to a 9V 100MA power adapter nothing seems to run.

I have two servos, an LED, and a WII nunchuck connected to the Arduino... Can anyone think of something that I can do to correct this?

Thank you.

The first thing to do is rule out the 9V adapter as the cause. Try running it off of a pack of 4 or 6 AA batteries and see if you still have the same problems. If you do, then it's a problem in the wiring or programming. If not, then the 9V adapter is the cause and should be replaced with something better. Don't use a 9V battery as a test replacement power source. You need a battery pack that can deliver enough current. The USB ports on a computer are rated for up to 500 mA. So you may just be pulling too much current from the 9V, 100mA adapter.

Actually, I believe that is exactly the case... This page: http://www.arduino.cc/playground/Learning/WhatAdapter says 250 MA or more...

Thanks for your help.

That adapter is hopelessly inadequate to the job: even micro-sized servos are likely to overload it.

It's always a good idea to power motors from a separate supply: they generate a lot of electrical noise that can cause reliability problems, and big ones are likely to overtax the Arduino's onboard voltage regulator.

These days, you can get a 5V regulated power supply that's good for a couple of Amps for $10 or less. I recommend doing that, and wiring up the servos with their own supply. Especially if they're going to be doing any heavy lifting or spinning.

Be sure it's a regulated supply: the really cheap ones will put out a voltage much higher than the nominal one if they're not fully-loaded, and might damage the servo electronics.