I guess - just guess - the machine has an over-heat safety cut out - it operates because it's getting too hot - it gets too hot because the cutting blades are gummed up with plant juice and have become sticky - the motor is being asked to do more work to overcome the gunge.
You might consider dismantling the blades from one another and giving them a good clean and a light oil.
See what happens.
Good Luck..., April 2016
