i bypassed the lid switch with everything assembled (except outer cabinet) and watched the clutch spin while the basket does nothing.
If the clutch is spinning then the gearcase is doing it's job.
There could be something caught between the basket and outer tub that is keeping the basket from spinning.
I have also seen nails and such things get stuck in one of the holes in the basket and grab the outer tub keeping it from spinning.
Get a flashlight and look at all the holes in the basket to make sure a nail or something is not caught in one of the holes first.
If you don't find anything there then I would remove the agitator and then the basket to have a look.