1) Have you set the clock. It sounds daft but is in the instructions to get the oven to work - and is necessary
If you have done this already, then I have just had a similar problem with my AEG Competence 5208 B.
It took a bit of tracking down but it appears to have been the one shot themal fuse.
This is a safefy feature that can occasionally blow (a quick internet search will give you more details).
Mine was located in the bottom left of the casing (with the back panel off), in a plastic sleeve and bolted to a small mounting post. It does not look too impressive (very small) but it can stop the whole show.
I got a replacement and crimps (this is important, it should not be soldered) from TDSPares on the internet, but Maplin do them as well (70pence). You will need to check what rating it is - written on the casing.
It took about 20mins to change - once I had found the problem, and appears to be okay now. You might need an electrician of course...
Yoodle, February 2008