I think you are confusing "nanotechnology" with "cold fusion".
Nanotechnology has the potential to make dramatic changes to how some very important things get done in our world.
One example might be in the creation of food. Almost all of the food we eat is created by some other animal or plant. The process by which such food is created is determined by what is useful to that animal or plant and not on what is most useful to humans.
In the future, carbohydrates, proteins, sugars, and fats may be created in giant vats using "nanomachines". Bacteria may be harnessed to provide part of such machines, but the process of making the foodstuffs will be designed to efficiently create "food".
Pharmaceuticals and other useful chemicals can also be created this way.
I have read descriptions of using DNA to accomplish decryption using a massively parallel approach. Computation in general may be furthered by nanotechnology.
Another post describes using nanotubes to create improved video displays. Imagine such a display which might be manufactured using nanomachines. It might not only be inexpensive to create but possible to repair using nanomachines. No more dead pixels.