Serial Port Unrecognized, Possible Short of Reset Circuit

I have been using my arduino uno SMD r3 to control and log data for my weather station project. Recently switched from a 6V to a 12V power source. When hooking up to VIN pin, touched the positive lead to metal on the SD shield and a "pop" and a flash ensued. Now arduino is unrecognized by my computer, and the correct Serial Port will not show up.

I tried hooking up another arduino uno I found around, and the correct serial port shows up but it will not upload sketches. This is also after hooking up to the 12V power source. After thinking this pb-acd battery was a arduino eating machine, I checked the voltage on the multimeter to get a value of around 12.5V, not too high, and not low enough to indicate a serious short.
The error message that I get when I try to upload sketch on the 2nd arduino is as follows:

avrdude: stk500_recv(): programmer is not responding

Has anyone experienced this before?

Sounds like you may have zapped the USB circuit in the PC as well.
Connect Reset to GND, and connect D0 to D1 (i.e. Loopback Test).
Open serial monitor, should see typed text echoed back.

On the 2nd board - you're sure it has a bootloader and you are selecting the right board type in the IDE?
Try press & old the Reset button; when the IDE shows "compiled xxx of 32xxx bytes" release the reset.
If you select File:Preference and turn on Verbose outputs, can be easier to get the timing of it correct.