I'm sorry for the miscommunication. I meant that I power the motors ONLY by using a 9V battery. I just used an alkaline battery to see how they would work while not being connected to the computer via USB. I posted another forum message about how to power all four motors, and they said that I should use four rechargeable batteries.
But anyway, I did find another code for the wheels that is working fine, so the servos are remaining.
And I apologize again for the misunderstanding with the schematic. That schematic from the link was what I was using before (without the power connections) before I found another code to use.
And yes, I am using an Arduino UNO.