Why does my loss value start at approximately -10,000 and my accuracy not improve?
You are using the sigmoid activation function on the output layer that squashes the values between 0 and 1, but you are setting the targets outside of that range. I suggest scaling your outputs between 0 and 1 for each output unit. By the way, using a library like conx that is built on Keras would give you a warning about this very issue. For more, see: http://conx.readthedocs.io/en/latest/Getting%20Started%20with%20conx.html#A-Simple-Network