You may have a broken motor coupling. Failure to agitate or spin accompanied by the sound of the motor running with no tub action are some of the symptoms you can experience with this problem. Just to be sure...the following link explains the symptoms of a failed motor coupling and how to diagnose the problem:

http://www.fixya.com/support/r3965207-whirlpool_top_loader_no_spin_problem

If you determine the coupler to be defective, the next link explains how to access the coupler and replace it:

http://www.fixya.com/support/r3574231-replacing_a_motor_coupling

The part number is included in the instructions I provided. Replacement parts (if required) can be purchased at any of the following websites:

searspartsdirect.com
pcappliancerepair.com
appliancepartspros.com
repairclinic.com

All these sites are reputable and offer great service with competitive pricing, so shop and compare. The first three sites I listed also include helpful exploded view parts diagrams to assist you in locating and properly identifying the parts you need. If you do not wish to order parts on line, use the part numbers I provided and go to your nearest appliance parts retailer. The coupler is commonly sold as part of their in-store inventory. The average cost of a motor coupling is about $15.

If you have any questions, please post back and let me know. I hope this helps you.

Broken cupler between motor and tranny