I hear the timer running but its not doing noting why?

What kind of timer? Can u post a picture?

Some timers have removable trip pins to adjust on/off time. If trip pins are missing, timer will run but will not turn on or off.

Some have slide pins which u have to move to turn on/off.

To may variables without more info and pics.

Chuck

Sometimes the timer motor is running but the gears are stripped.

Replace the timer.

I agree, gears can fail but the motor still runs. I'd replace it and consider a fully electronic one depending on application and location.