I accidentally shorted the 5v pin and gnd pin on my Arduino nano while powering it with 12v external pwr supply. The board made a pop sound and the voltage regulator outputs 9v at the 5v pin. Atmega heats up when powered with 12v external. While trying to upload, the RX led lights up faintly but no uploading.
Get a new one. You don't know which damage is done except for the voltage regulator. So fix that and you probably will find out that the 328P and the TTL-to-USB did not survive the 9V.
I had some 7805's laying around. I replaced the regulator with one of them. And you're right I fried it. Thx 
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