Washtub drum is not turning but I can hear motor running.

http://www.appliancepartspros.com/frigidaire-shock-absorber-kit-5304485917-ap5590192.html

sounds like the drive belt remove the front panel and look under the wash tub for a broken belt

Taking a guess is all that is possible...

The drum bearings have seized.
Something has broken and jammed the drum drive pulley.
Something has become jammed between the washtub and drum.

Your next step is to remove the top of the cabinet and examine the drive, ensure the motor still spins ok and the belt is intact, pulley not broken, etc.

If you find nothing wrong the task becomes fairly major as the cabinet will probably need dismantling in order to remove the front of the washtub for a closer inspection.

SOUNDS LIKE YOU HAVE A PULLY ON THE MOTOR SLIPPING IF YOU CAN HEAR THE MOTOR RUNNING, BUT THE DRUM DOES NOT TURN. IF NOT THE PULLY, THEN THE BELT MAY BE SLIPPING IN THE PULLY, BUT THE PULLY IS TURNING. THEN A NEW BELT IS NEEDED. IN EITHER CASE YOU WILL NEED TO ACCESS THE MOTOR AREA TO SEE WHATS HAPPENING. MOTOR COULD BE NOT RUNNING, EVEN THOUGH YOU HEAR A HUM IN IT. BUT, MOTORS NORMALLY RUN LONGER THEN THE LIFE OF THE DRYER.

Can you hear the drum motor running when you switch the machine on? You should hear it running and stopping periodically.
If the motor is running but not turning the drum then the drive belt is either broken or has become detached. It can be replaced by gaining access to the back of the machine.
If the motor is not running then it could be one of several problems - programmer mechanism not working, motor burnt out, motor brushes need replacing etc.

the belt may be broken, it wraps around the drum and the motor. See if you can turn the drum by hand, it should turn with little difficulty. Start dryer and listen for motor, if you hear motor running the belt is broken.

From your vague description, you can hear the motor running, but the drum will not go round......
I think it is possible that the belt drive from the motor to the drum has broken, normally located on the back of the drum

If you can hear the motor running but the drum is not turning, the belt maybe slipping or broken.
See section 7 of this:
http://home.howstuffworks.com/how-to-repair-a-dryer.htm
If you cannot hear the motor running then the door switch is not engaged or the motor is disconnected or dead (not too likely).

Sounds like the belt that turns the drum has broken. the hum sound is the motor turning. Does it still get hot in the drum? If so then you need a replacement belt ($15-$25).You can open the rear or the dryer to confirm the belt is broken. Be sure to unplug from the wall outlet to avoid electrical shock.

If you can hear the motor running when it is turned on then you dryer needs a new belt. If you cannot hear the motor running it needs a new motor.