Did I fry my Arduino Uno's USB connection?

Development Tools IDE 1.x
1

I dumbly connected a 9v battery to the ground and 5v pins instead of ground and Vin, while my computer's USB was also plugged in. This turned off my Macbook Air. Now, the port to the Arduino UNO is not showing up in the Arduino app in OS X. However, the last program I loaded on the Arduino Uno still works (pressing a button to light up the onboard LED).

I've tried rebooting my Macbook and pressing the reset button on the Uno, testing/changing USB ports on my macbook.

Did I somehow damage the USB connection on the Uno?

2

You know, it's better a fryed 20€ Arduino Uno than a 1000€ MBA!

Honesty I don't know if the problem is in the Arduino usb interface, but it's a good practice to hook up things when everything is turned off!

3

and also doble check the main voltage conections.

4

Yes, you more than likely fried the 16U2.
If the 328P feels hot at all to the touch, it is also damaged and will just be a matter of time until it stops working.