There are a few problems possible. Assuming that there is not a mains (house) power problem, use the following logic to sort out the problem:
1. Do you have a light (assuming that the light bulb is good)? continue to #2.
2. With the machine unthreaded, the presser foot up, and the power cable plugs fully plugged in at the motor and foot control, depress the control to the run position.
Carefully bend and wiggle the cables at the plug locations one at a time. If the motor runs, the cable wires are damaged so you will replace the cable.
3. If available, try a (known good foot control) from another Bernina 830 of that exact vintage.
If the test foot control runs the machine, replace your foot control. Note: If the foot control is a type 213 for very old models, suggest that the control be replaced with a two wire electronic phase type control. (requires the foot control plug end to be cut off and rewired to the new phase controller). These electronic phase controls can be purchased from EBAY. Stay away from the Bernina type 213 control if possible. The type 213 controls have not been available for many years and it is highly likely that these controls are in a used condition, so you will not know if it has been properly adjusted.
If the 830 is a later model machine with the type 232 or 290 foot control and it is determined to be defective, no problem as they can be repaired.
4. If the (known good foot control) still does not work, you can assume that the motor has a problem. Motors for the Bernina 830 are occasionally available on EBAY and other sources.
Note: If the motor brushes have worn out and the commutator has been damaged, the motor is also salvageable.
Note: Always unplug the machine from the mains power when not in use as per Bernina instructions.