If your top-loading washer will not rotate or agitate your wash, and you can turn the top of the agitator without turning the bottom of the agitator, then you may need to replace the agitator directional cogs (also known as agitator dogs or dog ears). These cogs or dogs are made of hard plastic and can wear out over time.
WARNING! Before attempting to work on any appliance, make sure that all power (electricity) and utilities (water and gas) have been turned off and/or disconnected on the appliance. Read this before you start any repair.
This is a relatively easy repair. To access the dogs, remove the soap dispenser from your washers agitator and use a socket wrench to remove the bolt that secures the top part of the agitator in order to access the agitator cam and dogs. Use a flat-head screwdriver to gently pop the old dogs off the cam. Make sure the new dogs match up with the curve of the agitator cam.
You can even buy an Agitator Repair Kit which comes with cam-thrust, spacer/bearing and four agitator dogs in case other parts are worn and need replacing.
Find new agitator dogs using your washing machine model number which you can locate here. Or visit http://www.everyappliancepart.com/Category/Washer-Parts/Agitators