I can't stand a conceited (stuck up) antenna. Sorry, couldn't resist : ). Anyway, do you hear a clicking sound when the antenna motor is running? There is a nylon cord that pushes/pulls the mast up & down. If the mast is simply stuck you will hear a clicking sound as the nylon cord grips and breaks loose trying the move the mast. In this case check the mast for any dents or bends that could be binding it. Also oil the mast with WD40 on steel wool. Try pushing the mast down manually while someone else pulls the knob. It can't be lowered unless the motor is winding up the nylon cord, If you don't hear a clicking the nylon cord or something else may be broken. In that case, you would need to remove the antenna and open it up to investigate. Do you have a shop manual? Instructions for removing the antenna are there.
Often the nylon mast will break and can be replaced
The motor makes a clicking sound but nothing moves in any direction if broken
If the nylon mast is not broken I would think the motor that pulls the mast down ( and up ) WB the issue and requires removal inspection repair or replacement of parts or the unit
You can get a new antenna mast from CaddyDaddy.com I use them all the time.