Sounds like you burnt out the motor inside. If you wanted to feel the weight move around, that's probably the small amount of G-force added to the spinning disks when they speed up faster than the motor can spin them.
Inside a Hard Drive are a certian number of hard disks (no idea what there made of or what there covered in) and a few "Arms" which extend to a head which is really a laser. These "arms" move to read and write on the disk. There are about 2 arms for eash disk(one for either side of the disk) so there could be as many as 4-16 heads or more in a single Hard drive. Therefore the disks have to spin. Hence the motor. If you spun it for 3 minutes you spun the disks faster than what the motor was spinning at(could have even been in the wrong direction) which would badly damage it.
Hope that enlighten you. I got all that info from taking apart a old 20Gb HDD. ^.^
