Firstly, how old/big is the tree? When was it planted? What is the site like? We'd need to know that sort of info before any advice/conclusions are made or come to. Possibly the end of the tree, but further advice can only be given after knowing more. And don't grab at 'ash die back' just because it's recently hit the headlines!

we had a similar problem some years back and eventually had them removed as they were in a hedge along side a road. Made very good logs......

Planted the tree the spring of '06. It's done very well and grown nicely since then until last year. We're in MT, so winter can be harsh. Soil is clay - i hate it, but did try amending as much as possible back when i planted it. It's a nice tall tree now and i'd hate to have to dig it up, but there just doesn't seem to be any life up above the first couple of feet from the ground.

It's a poor time of year to be without leaves. My guess is that it's had it. Even if there is any sign of green under the bark higher up it's not good. Ash are pretty tough and would ride out most things. Sounds to me like a problem at root level. What species and cultivar is it?