Hi,
There could be 2 things that effect the hob coming on,
1.The fuse has gone (check your cooker manual, if its like ours a STOVES, it has a seperate fuse.
or
2.You need to ensure that the 'lid' on the cooker is far enough back. There is an automatic cut out switch that activates if the 'lid' is not back. (I had same the problem, we used to use a dish cloth wedged under the top cupboard to keep the 'lid' in position).