128,
Not much you can do..
When you first put the unit in the water and turn it on, it should run through a quick self test. It will move forward a little and then backwards a little. If it stops after that, it means it has failed its self tests... If it does not move at all, then it is not even doing the self tests...
About the only thing the owner can do is make sure the suction motor at the top is blowing out water and not gummed up with hair or something.
Other than that, turn in a warranty claim..
Thanks,
Jim R.