So, I did a very stupid thing and accidentally put 12 volts through to the 5V output in on my Uno.
I didn't keep it there for long, maybe 5 seconds total, but I started to smell a small bit of "overheating electronics" and quickly realized my mistake and the pulled the power.
Sadly now, it doesn't want to be recognized on any computer and all lights stay steady on when it is plugged in via USB (RX, TX, L, and ON).
Is there any way to save it? Or, is it toasted?
Try the loop back test (see Sticky at the top of the page) but assume the worst.
dannable:
Try the loop back test (see Sticky at the top of the page) but assume the worst.
Tried it but on Linux nothing mounted and I couldn't open the serial monitor and nothing showed up in the Serial Port section.
So, sigh, I suppose I will have to get a new one. Hope I didn't fry any of my sensors in the process 
Hang on to the 328, it may be 'walking wounded' - try it in the new board to see. But it is unlikely. I've had processors overheat to the extent that I have burnt myself touching them but they still function afterwards. But I mark them so I know that they are now dubious!