how can i make my oven work ( kenwood)?

Obviously the problem is not the element since you have replaced it. I would say that there are two possible causes why the element won't heat up.
1) The switch that controls the heat for the oven might be faulty, so no supply is reaching the element.
2) It might be the thermostat, when these break the normaly revert to an open (off) state preventing power going to the element.

An electrical multi-meter is needed to test these.
CONSULT A QUALIFIED ELECTRICIAN IF YOU ARE UNSURE OF HOW TO TEST THESE ITEMS - SAFETY FIRST.

Russ
March 2010