Sarah,
The problem is the overheat sensor has tripped. You can reset them but you need to remove tne rear panel coevering the heating element.
you are looking for a small circlular sensor (about the size off a penny) with two wires connected on either side. There might be two or three of these near each other. One will have a small hole in the centre, if you poke a pin in the hole you should hear a click as it resets, remove pin!! reassemble and test. If it keeps tripping they may another problem causing it to trip but mine has been fine since I reset it.
They never say on these sites but please make sure you switch the electricity off before you start
Anthony Edwards, April 2007