Baking Disaster!

Three ruined cakes in four days!

 

I have always enjoyed baking, and have not been too bad at it. We have a tradition of giving home-made cakes to friends for Yuletide gifts.
So, I made the first Dundee cake. Good. Then the second - not good. Burnt. Hmm. So I made the first Ginger cake. It sank! I hadn't opened the door during the baking, so what was going on?  I have bought a new oven thermometer, and checked the shelf position. The third Dundee was made, and put in... and that sank too!
I am really cheesed off, more than a little bewildered, and not baking for the foreseeable future.