What would have happened if the nazis completed their wonder weapons before starting WWII?

The world would almost undoubtedly be under its 8th decade of Nazi rule, and Hitler would have created the greatest empire in the history of the human race (greatest as in largest and most powerful).

A list of their proposed Wunderwaffe can be found on Wiki (Wunderwaffe). A brief glance down the list will reveal some truly extraordinary weapons which, if they had been built, would have ensured a very swift victory for the Nazis in WW2.

The Supermarine Spitfire would be no match for the Nazi jet fighters and bombers. The Battle of Britain would have a been a brave but futile show of resistance resulting in the quick annihilation of Britain's air defenses. The following land invasion would have quickly lead to the capitulation of Britain allowing the Nazi's to fully concentrate on the Eastern front.

The conquest of the USSR would have been a formality. The incoming shells from the feared T-34's would have done little more than give the Maus', Lowes, and E100's a new target to aim for. Any pockets of stubborn resistance could be quickly and brutally snuffed out with either a salvo of Nazi rockets like the V3, or blasted from above by jet-engined bombers. Considering how close they came to taking Moscow with conventional weapons, I've no doubt Moscow (and Stalin) would have been fallen well before the game-changing winter set in.

Britain, mainland Europe... where would Hitler turn his eye to next? America!

At this stage the States would most likely be suing for peace if they had been so foolish as to declare war (very unlikely given the circumstances). It would be pointless to continue the conflict. The chances of launching a successful invasion across the Atlantic would be next to zero. The Type XVII submarine  would have been light years ahead of anything the Yanks had in 1940. No, a US invasion would have been completely out of the question. Anything that survived the Type 17 U-boats would have had to survive aerial bombardment from jet-bombers and V weapons. The few stragglers that remained would crawl ashore to find themselves facing the full might of the Wehrmacht in all its terribly glory.

In all likelihood the US would never declare war in the first place. This opens up a whole new can of worms... Would Hitler declare war on the new world? If so could the combined forces of the Wehrmacht and Japan take the States before the completion of the Manhattan project? If I had to guess I would imagine that Pearl Harbor would still happen (Japan would still want to expand). But the US wouldn't reach out to exact revenge. It would fight a defensive battle, ever weary of a war with the all powerful Nazis. I suspect Hitler might play peacemaker, the US would coincide territory to Japan, and the path would be paved for a gradual fascist cultural take-over of the States. If they did develop the bomb in time, it would usher in a new cold war, one that an utterly isolated America would probably end up losing.

But, all this ignores the fact that most of these Nazi wonder weapons were created to counter advances made by the Allies during the war. That said I think if the Messerschmidt Me 262 alone was operational on the outbreak of war -it would probably have tipped the balance of the war in the Nazi's favor (total air domination). 

They had no wonder weapons this is an unproven conspiracy theory. Their rockets were way of being remotely effective and had no guidance, which is the only reason rockets are effective. German technology was no further ahead than Russian or British, they just spent more money on each product which ended up being a huge disadvantage.