Your problem is most likely to be due to an element which has gone.Most fan assisted ovens usually have the element with the fan at its centre. These usually will only last around 3 years depending on the cookers use.
These are usually easily replaced providing you are confident at carrying out such work. If you know someone who is a dab hand at electrical repairs this can be done quite easy. However you may have to remove the oven. On many ovens i have worked on it is just a point of removing a plate which covers the fan and the element. Once the cover is free you simply undo the retaining self tap screws that secure the element to the cooker. MAKE SURE THAT THIS IS ISCOLATED FROM THE MAINS. PULL THE FUSE AT THE CONSUMER UNIT OR SWITCH OFF ALL THE MAINS IF IN DOUBT! Now with the power totally off from your cooker remove the element carefully and unclip the two wires on the back. The earth lead may need to be unscrewed. It is then the total reverse of removal to fit your new element. Again quote your cooker and model for correct element you will get one from ebay or off the net.
carlito corway, November 2010