Your oven should be connected to the mains supply through a 13 Amp 3-pin plug. This is probably plugged in under the worktop, inside an adjacent cupboard. Switch off the socket. Pull out the plug, remove the cover and take out the cartridge fuse. Replace it with a new fuse, check that all 3 wires are secure and intact (not burnt), and re-insert the plug. Switch the socket back on, and try the oven.
If you still have no joy, call a repair engineer.
DavidCH, June 2011