How might the outcome of WW2 have changed if the D-Day invasion had not been successful?

By the time the D-Day invasion occurred, Adolf Hitler was becoming more and more unstable in his thoughts and actions. He had visible signs of Parkinson's, and has been posthumously diagnosed with schizophrenia, drug addiction, and manic depression.

This was a psychotic man who had enormous power.

He was actually very pleased with the (beginning) D-day invasion because, as he said "we could never have taken the British in their own country, but now, they have come to us!".

Because the D-day invasion was a success for the Allied forces, Hitler realized that his troops were being over-run, and thus, began to realize that the war was coming to an end, and he was not the victor he thought he would be.

The failure of D-day for the Allied forces would have meant an invasion of England, and possibly even America!

There were U-boats that were approaching America, and Hitler and his scientists even had more advanced weapons that were in development to utilize. He also had recently come into possession of the American "mint" plates, which could have flooded America with counterfeit money, thereby destabilizing our entire economy, which would have been a disaster of epic proportions.