AZKAT,
Which gears?
If the motor turns, then does the main shaft turn? Is is locked up solid, or will it rock back and forth?
Did you check for thread or debris under the bobbin hook and that area?
Did you check the TWO gears under the covers on the bottom of the machine, and the one at the top in the pillar that drives the vertical shaft. They need grease, not oil by the way.
Did you check for thread binding the machine up? Been there done that more than I care to contemplate.
Lots of things to look for. It could also be a lack of oil as well.
Joe