Dirt Devil foot device doesn't work to turn vacuum off

Yesterday I assembled my new Dirt Devil Featherlight upright vacuuum. It was working great for a while and turned off and on just fine. All of a sudden it wouldn't turn off or on any more so I had to resort to powering it on and off by unplugging and replugging it. Please advice...it's brand new. The small square foot pedal seems shaking but otherwise is on securely and I don't want to risk breaking it off by tampering with it. Please advise.