Thank you so much for your help. indeed, the brushes of the electric motor were rusty and did not move. I took off the motor, cleaned and replaced the brushes. the forklift is working now. but there is one more question. When the ignition is turned on, the buzzer gives several beeps. but there are no errors and the loader is working. What can this mean?

Thank you so much for your help

Hey DemianM, as it is a DC motor I would seen for the drive motor brushes first.
Look at the drive contactors as well but normally it would give an error number if that is the problem.
Marcb