AC current kills Arduinos and Computers

I intended to use a hacked kill-a-watt meter as it was done here and use the current and voltage readings from it to make the DC motor react to changes in these variables.

I tapped some wires into the device as instructed in the mentioned tutorial, I plugged them into the corresponding arduino pins. I had the arduino plugged into the computer via the USB cable when I plugged the kill-a-watt meter to an extension cord I had prepared, BOOM!!! instantly sparks, noise and a smell of electrical shortage came from the experimentation scene, my computer went black and the lights of the arduino went off. Both are dead and became bricks in a fraction of a second.

Not having an extra arduino my hopes of creating a project were slim. I sorted through my electrical parts and I found a PIR module. This module outputs a LOW HIGH signal when a change in its IR sensor is detected. This output was used to trigger the transistor which controls the DC motor. To the motor I attached a string to its shaft and with a weight on the other end. The motor drives this string creating a visual cue that a change has occurred in the scene.

Here is a youtube video of the contraption: http://youtu.be/I2DWZwbiQrs

I have ordered a new arduino. I am uncertain as to when I will be able to fix/replace my computer.