Check the foot control - they can get trodden on and bent - unplug it and try the action in your hands - if it is resisting so that it can't be pressed down just a little and so give a very slow speed try taking it apart and check for bent metal. Putting some grease on the hinge would be a good idea, if it has no lubrication.

If, when you press the pedal there is a buzzing from the motor but the machine does not start to sew then the inside of the machine is probably in need of a clean and oiling.

I find gun oil is very good for sewing machines.

It is not unusual for bits of thread to get caught in the workings under the needle - where the bobbin fits. Do take it apart and brush out fluff and check for thread. Just how often depends on the amount of work it does. If you keep it clean and oiled it will last far longer and work better.

I used to do repairs and servicing of knitting and sewing machines, and often earned the whole fee just by applying a tablespoon full of solvent and maybe ten drops of oil. Well - there was usually a lot of mopping up of dirt and brushing out of foreign object debris as well, but basically the machine wasn't working because it needed to be cleaned.