I plugged in my Arduino the other day and was able to upload new sketch programs to it. After modifying one of my servos (modified it for continuous rotation (see youtube video here: How to hack the TowerPro MG995 Servo for continuous rotation - YouTube)), plugging it in the Arduino and successfully running the program, the Arduino board will no longer connect to Sketch using the USB cable.
The other other thing I did was connect a 9V battery into the Vin and neighboring GND pins on the Arduino. When powered by the 9V battery, the Arduino seems to function perfectly.
But, when I disconnect the 9V battery and plug the Arduino back into the USB cable it powers up and begins running the last program. But, I can't upload new programs via Sketch. In Sketch under Tools -> Serial Ports menu, it's missing the USB tty ports.
I'm new at working with Arduinos and quite stumped. I've posted a picture of what I'm seeing below.