Quoted from LTG:
Start with the basics. Outlet you plugged it into working right and grounded ?
home wiring is tricky. even if you did install/ground the machine properly, that does NOT mean you are protected.
most home fuse boxes run the return and ground to the same buss inside the box, "the return buss". not sure why, but it allows hot AC to appear when the power is shut off.
the best way to be sure, is to look at your box inside. you can see if any bare "ground" wires are tied into the return buss.
also, if you live in a hot area, your ground rod,"assuming you have one". will float due to the ground drying/schrinking.
it is recommended that you water your ground around the rod, to ensure you have a solid ground.
I was working on a Dodge city. it had a double switch installed that opened hot and return. So I felt safe...HA!!! it shocked the s#!t out of me too. lesson learned, unplug it!
And, as Boilerman said, chk that fish paper in the door, it is your only safety.