What is going on with my arduino?

I was working with a servo which needed 12V, I dont know what happened and my PC turn down, when I realized a part of my arduino had a kind of sparks, so I unplugged the external alimentation, now, when I plug my arduino, leds TW and RX are always on but my PC doesnt find the usb conection. PLEASE HELP

Show us how you had it connected. A clear drawing by hand and photographed will do.