First I would check to see if the grower used nylon string to tie up the ball. Just push some soil from the crown and look for a string. If it isn't rotted by now cut it away. Be carefull not to damage the trunk.
Second, if you planted it, was it a potted in a plastic container? If so, the roots may not have been properly, how do I say, sliced-up. Roots in a plastic container may keep growing round and round if they are not properly re-routed.
You have to dig up the plant if this is posibly a problem. Or find a way to slice into the soil to cut the roots at where they were when the tree was first planted. I would recomend a professional for this job.
Could be borers, also. Look for their entrance holes around the trunk. Once again if you see places where little bugs could have gotten in, you need a professional. It is hard for even a pro to get rid of borers.
Send some pics. It's posible it just needed water after the dry March we had.
