Arduino Uno r3 loop back fail: dead Arduino?

I'm new to this forum...

I've had this Arduino for a few months now, and it's always worked well.
Yesterday I was running a test and at some point I tried to upload a sketch and I got the avrdude error:
avrdude: stk500_recv(): programmer is not responding

I looked up what could be the issue but they couldn't be drivers of course, since I have always used them with this board and I can upload fine onto any other Arduino.

I tried to run the loop back test and it fails: when I turn it on: the L LED is steady on, and if I send something to the board the RX LED lights up, but I get nothing back. The TX LED is always off.

Now, I am inclined to believe that I must have burnt something yesterday by accidentally sending a high voltage to a pin, but I just wanted to make sure that there weren't any other options / tests to run to possibly fix this.

Thank you very much!

The ATmega16U2 may have forgotten its purpose in life. Try reflashing...

"accidentally sending a high voltage to a pin" is usually a pretty good way to kill things.