The machine stops working and the handle will not turn

Make sure you have properly lubed the machine ... your trouble is likely lint buildup or a scrap of cloth blocking the rotation of the mechanism under the machine ... you will have to take off the sole plate and remove anything that shouldnt belong there .. if that is not enough you may have to remove the bottom and check ... make sure the needle is going thru the sole plate hole and clearing the foot ... if its not then check for a bent needle or one that is in backwards (with respect to the flat side) .. you can check the motor to make sure its working ok by putting the machine in the bobin winding mode .. that disconnects the motor from the internal mechinism ... only the handle should turn in that mode ..