Hello Lizinka,
I think this is a problem with a worn rubber wheel.
Dismount the hand wheel at the right side (you have to use carefully 2 scew drivers as levers after you have turned off the central screw). Then you can dismount the cover at the right side (3 screws). Now you can see the motor. Operate the lever at the back side, next to the motor (with the small wheel at the end). So you can see the motor bobbing. In the upper position the rubber wheel at the top of the motor is moving the stitch-mecanism, in the lower position the rubber wheel at the bottom of the motor is moving the shaft for loading lower thread rolls at the back of the machine. The rubber wheel at the bottom usually is in good condition, so you can check the function of the motor. If it is running in lower position but not in upper position, you have to replace the rubber wheel at the top.
Let me know, if you have further problems. I'll help.
Let me also know, if you want to sell the machine.
Dieter
March 2010