Q.nectarine tree
My 2 year old nectarine tree was doing fine. Flowered and had leaves on it. Now there are no leaves and no sign of life. What should I do.

Are there signs of pests or disease on the leaves, branches or tree trunk?
If you bend the branches do they snap off or bend? Dead branches will break off.
You can do the scratch test to check on the trees health.
Here are some links that will help you and list some of the common tree issues.
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm
https://www.gardeningknowhow.com/edible/fruits/nectarines/growing-nectarine-fruit-trees.htm
https://www.gardeningknowhow.com/edible/fruits/peach/common-peach-diseases.htm