What causes my drum not to turn in my washing machine?

My old KitchenAid Prestige, model KAWS677EO0, serial # CF4613915, is not working. The motor strains but the drum does not turn. The agitator seems okay on the top although the bottom portion may be troubled. Can the answer be as easy as some small clothing item getting wrapped around under the bottom of the agitator? If not, what might be wrong with our old machine?