why does my Belling cooker lose all power when I try to swich it on?

I have a diplomat 110 duel fuel cooker. When I try to switch on the grill or oven all the electric on the cooker goes dead, including clock and igniter. After a while the clock comes back on. No fuses trip. This happened before, and I checked that there wasn't a loose wire in the back. It was then ok for a month or so and now its doing it again. Any ideas?