Yes, that's the temperature indicator, it goes out when the desired temperature is reached.
This is normally a failure of the circular element.
Isolate the power to the appliance before working on it.
Inside the oven, take out the rear panel, this is held in place by a few screws (normally).
This will reveal the element and the fan.
If the element is obviously damaged, obtain a replacement first.
Take the screws holding the element in place out and carefully bring the element and wiring into the oven cavity. Swap the wires onto the new element and fit it in place.
Refit the cover, restore the power, set the clock if necessary and try the oven again. You should now have heat.
If the element isn't obviously blown you'll need to take it out and test it with a multimeter to check if it has failed (if you don't have access to a multimeter you won't be able to test the element).
If the element isn't screwed from inside, take the cooker out and take the rear panel off, you'll find securing nuts on the rear of the element. Take these off and it will release the element.
Hope this helps
Let me know how it goes.