Mixed up wire color from ATX PSU, and accidentally sent 12V into the 3.3V pin on my Uno.
I put a new ATMEGA chip in it, but still no life, and no serial connectivity. Its my very first arduino my parents got me as a gift years ago, so it has a certain sentimental value. Any chance of getting it running again? What all would need replaced in this instance?
Then I think the ATmega16U2 is damaged an possibly the regulator as well. You can change both but you need to solder and both are SMD.
I would say, lesson learned, hang it on the wall and by a cheap new Arduino 
Yeah, I thought the USB chip was probably shot; bummer. I'm no stranger to SMD soldering, but that ATmega16U2 has a LOT of pins!! :o
I've got literally heaps of 'duinos laying around; I was just really hoping to get that one back up.
Yuh, and an exposed pad in the middle. Meant to be soldered in the reflow oven; could be done with hot air too.
I've heard of people here trying to repair those, and switching out part after part (using hot air, I assume) without ever getting it back to life.