Find the operating instructions and inspect the accessible sink, cabinet and connections before starting. Look for damaged controls, loose parts, signs of leakage and material left in the opening without reaching into the chamber.
What the observation tells you
Long inactivity does not prove that the motor or drain is clear. If the appliance's history is unknown, a cautious assessment is more useful than a trial with a large load of food. Follow any model-specific guidance for returning it to service.
A useful next step
Arrange an inspection if the mount, water path or electrical arrangement looks doubtful. Resume ordinary use only with the required water supply and protective accessories in place.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.