Check the trunk from top to bottom - you're looking for soft or soggy or blackened areas. You'll probably find its soft at the top at least, but check the whole thing for other soft areas and wherever the lowest one is, cut the whole thing down past that point, even if that means right down to the ground. It should shoot from the roots or any remaining stem once you've done that - damage from the severe winter has caused the problem.

Give it time to shoot out, too. It may take until July to sprout. Light feeding with a slow release plant food, such as Growmore, will speed this somewhat.