Zanussi ZSA 10 not working?

We have a Zanussi ZSA 10 that is being very tempremental at the moment. Young nephew was playing with the buttons on the front of the oven over the Xmas holidays and since then the oven will only work for approx 45 minutes at a time. We have tried to check that it wasn't accidentally knocked it on to the timer etc but without any success, although we could be missing a trick here.

Once the oven has been working for the 45 minutes or so it switches off then takes a good 30-45 minutes before it can be used again.

Any help would be appreciated.