Hi,
I'm currently learning how to do PCB and stuff. I just did one to power and control LEDs from an Arduino with a MSGEQ7 to make it sound reactive.
As soon as I powered the PCB with 12v, the chip became hot so I unplugged it. But, it was too late. the Nano became unresponsive from USB, unable to flash anything to it. I double checked my schematic and my PCB with a multimeter but I can't find the source of the problem.
Also, are you using an Arduino Nano board or just the Atmel chip and if just a chip which one?
I am not certain but I think some of your pinouts may be wrong on your diagram.
If you have a multimeter then I would suggest you check the power supply output voltage.
If its over 12v then that could be your problem, personally I am sticking to around 5v supplies for mine.