I had a similiar problem with a brand new out of the box Dark Motor, when installed it would not move at all if the dish was attached to it,after a few attemps i did mange to get both the led lights to flash which at least indicated to me that it was getting power ok,i reflashed the image etc,it made no difference,i had bought it from the sponsor and returned it under warranty,they exchanged it no problem at all,when the motor was returned to them they bench tested it and it worked no probs (although it wasn't able to be tested with a dish attached),one thing i would say is that the led on the top of the motor never worked for me.
i am now on my second of the same model and again the top led is not working,it never has but the motor works no problem at all.I have searched a popular search engine for information on these faults with the dark motor and there were at least 3 other people with the same problems,perhaps a faulty batch??
just thought i would let you know of my experience with this paticular motor, hope it helps