Why will my Siemens HP 903 electric oven not heat up?

We noticed that the fan part of our oven had stopped working and was just blowing out cold air - even with the thermostat turned to full! We've thoroughly cleaned the oven and it's still blowing cold air through - even after leaving it on for well over half an hour! (normally takes 15mins max to reach 220 celcius!)

Any ideas what I can do? Any help would be greatly appreciated, and I can eat hot food again =)