Ok if the clock isn't on then the oven wont work as the clock sort of controls them.
What you need to do is pull the oven out and remove the back panel.
There you will find a few thermostats. They will have 2 wires going to them and are about the size of a 10p.
You need to check these with a multi meter and make sure they are fine as one goes to the clock.
But if the thermostats are fine then its looking like the timer is the fault here im afraid.
So check the thermostats out if you can and see what you find as for this fault its either them or the timer that's causeing this fault here.