Arduino UNO dead with CNC shield I have an Arduino UNO with a CNC shield. The Arduino is almost certainly a clone. 

I installed GRBL with no issue and I have assembled a jig with CD-ROM motors. My first attempt to control this with UGS worked no problem. 

I powered down to change the stepping with the jumpers and powered back up and was presented with a very hot smell after a few moments.

I removed the power quickly but now I can no longer program the UNO. It gets recognized in my devices but I can't send any code, even blink. 

The jumpers were set like many examples I have seen on the web so I don't think this was the issue. 

I am wondering if the way I powered it up was the issue? I am supplying the UNO with 12V 2A supply and I can't recall what order I plugged them in but I get the feeling it must have been supplying 12V to the Arduino.

I have now removed the shield and powering the unit solely from the USB and still can't communicate. 

I have resigned to the fact this board is now toasted. Is it important which order you plug in the Arduino? USB first? Do you think it will be possible to recover this Arduino.
This sounds as the ATmega328p processor of the UNO was fried. As the UNO has a second processor (ATmega16U2) which is simply a USB-to-serial converter you only see the presence of this in the list of USB devices but it cannot communicate with the board's main processor anymore.

The plug-in order is not that important with the UNO board only but depending on the components you have attached it may be important. especially if the circuit does not have protection against induction current, p.e. fly-back diodes.