dont mean to scare but you WERE shocked
its just so low of volts and amps you couldnt feel it. i have a custom PC that i took apart the PSU so it would be smaller(im building the smallest pc i can) i shock myself all the time on it when i work on it while its plugged in(ones you can feel) doesnt hurt and it wont harm you
guess im just stupid and crazy but dont be afraid of getting shocked by a computer
the most volts on a PSU output is 12V the amps are high but since your body doesnt "use" energy when you get shocked the amps are EXTREMELY LOW!
this is in part of because a PSU only uses the minimum amount of Amps\Watts as it can.