The power cord must be OK as the secondary brush roll motor is running, you have tested the switches, and assuming there are no other reset buttons apart from the one on the brush-roll (The DC17 is not a UK model so I giving "acquired-by-reading" and generic upright Dyson advice here as opposed to specific "from DC17 experience" advice), we must suspect the motor.
My next job would be to strip it down and bench test the motor.
Any US readers that know better, do please chime in.