Mountfield VE32 Electric Scarifier

Bought this scarifier from my local garden machinery supplier went home mowed all the lawns in preperation, plugged in the scarifier and all it did was hum. If I lifted the front up the blades then went round but as soon as I tried to scarify my lawn they stopped and the machine just hummed as though there was not enough power to turn the blades. The supplier came to look at it but said he would bring out another new one. Guess what, that did exactly the same thing so all that preperation for nothing, a waste of a day.....USELESS