My aquabot power box when switched on will hum a bit then power off.Suggestions

Probably the drive belt came off the pulley or the belt broke. Similiar to a vaccuum

humming noise from motor means it is seized

Well either you have a jammed up motor, or a bad motor, or the Controller unit has faulted.
http://www.robotshop.ca/PDF/aquabot-turbo-t2-manual.pdf
Above is a manual, this should help you it has exploded diagrams to help. There seem to be many ways that it could get tangled up, or maybe the belt has come off, any way it's about time to A: Get a screwdriver, or B: Call a service man....