Arduino UNO not recognized anymore

Using Arduino IDE 1.x
1

Hello, I have tried to connect 12V DC input to arduino UNO and from that moment my arduino is not recognized anymore by the computer, and also the reset button making no any effect.
When i put power on the arduino (from usb) the pin 13 led is always ON and also the ON led.
It looks that the arduino got stuck in some state...

In your opinion, my arduino was destroyed?

2

How did you connect the 12 V to the Uno?

3

pert:
How did you connect the 12 V to the Uno?

The arduino have Power jack, and I have 12v 1a adapter...

4

iSelector:
The arduino have Power jack, and I have 12v 1a adapter...

Was the Arduino powering any external devices at the time?