If the drum won't turn on your washer and you can't reset it by turning off the power and manually rotating the drum 4X to the right and then 4X to the left and then turning the power back on, it's time to replace the rotor position sensor (hall sensor). The job may seem more overwhelming than it actually is, it's really not difficult, but watch out for sharp edges on the inside of the cabinet, you may cut your fingers badly as I did :(
Here's all it take to fix the problem, remove the four screws to the access panel on the back, use a 17 millimeter socket to remove the center bolt on the back of the motor, pull off the cover, remove the six 10 millimeter bolts with a socket, remove 2 screws holding on a wiring harness at the bottom left of the motor, pull off the motor assembly and disconnect the two wiring connectors. Then simply snap off the position sensor and replace with the new one, reverse the disassembly procedure, and your washer will be turning and spinning again like new! You can also search for this problem on YouTube and find videos that detail the repair. Do it yourself and save hundreds!