If it has tripped out while it was on then its more then likely the heater element as blown.
If you reset it now i take it its running again? You will find though the heat will go as the heater isnt getting hot now as it will have blown.
To access the heater if you are looking at fixing this yourself you need to empty the oven and remove the back panel in there. From there you will see the heater around the fan.
If its blown you can sometimes see it as it will have visable blow marks on it. You need to replace it from there.
But from what you say this is more then likely the fan element has blown which has caused the problem here.
If you need anymore info just get back to me.