From my limited experience... there are 3 things are usually involved:

the switch, which sounds like it is working ( in both directions?)
the motor, which sounds like it is working
a cable that goes from the motor to the gears that actually move the seat

The cable can come loose or the hex head end can get rounded off.

It sounded like your motor was spinning in both directions, but no motion in one. I have had luck moving the seat by adjusting it while standing outside of the car (not sitting in the seat) and giving it a push.

The seat springs on my car were bad and I found a whole bottom end (spring section and motor section). There are posts here on taking the seats apart. Good luck.