Wireless arduino rover only works when plugged in???

I bought this... http://www.robotshop.com/productinfo.aspx?pc=RB-Rbo-89&lang=en-US

And its being a pain. I configured the wireless xBee, had it all plugged in, I uploaded the code on the website to the rover, and uploaded a code that sends a 'w' then delays and stops then repeats on the uno. So when i plug everything in nothing happens, but when i plug the usb in to the rover, the rover starts moving and runs the code on the uno, which is totally wireless. It doesnt make any sense. The uno is no plugged into the computer so i dont understand why the rover only works when its plugged into usb??

****I just plugged the usb into a charger for just power and it still does the same, so its a power issue, for some reason if there isnt enough power it doesnt recieve the signal, in know its enough power to move the motors, but when i unplug the usb a light flashes and it stops moving

So, what battery are you using? How is it connected?

Did you see the note about using a non-LiPo battery: "Note: If you are using the 4xAA battery pack, please remove the jumper located at the left rear of the board.

I removed the jumper, I am using 4xAA. I plugged in a 9v along with the 4xAA and it worked fine but i dont understand why it just stops working. If i upload a code for the motors to continuously run it does it just fine without the 9v or usb plugged in. Hmm.... Thanks for looking into it!