Be an arborist, and put some diagnosis onto the tree:
1. Look at the tree and see if it has grown any buds last fall.
2. Scrape the bark on a few twigs, see if it is green or sappy beneath.
3. Snap a few twigs; a tree dead all winter will snap off easily.
4. Get a good pair of binoculars or spotting scope and look for sunken, dried, or discolored bark; also look for buds in part of the tree that might be swelling with spring growth while other parts are not.
5.Look at the trunk and root zone of the tree for any probable reasons to fail.
6. Evaluate the entire area; are other nearby trees in good health, or is there evidence of chemical or environmental factors that might have killed it recently? Salt damage/snow piling is a common cause.