Hello! I'm new to this forum and really need some help!

I have had my chinese elm bonsai for just over a year now. The first few months were great! It was growing perfectly and I kept it well trimmed! However, come the winter months I noticed it started drying out much quicker than usual and the leaves would fall of and it wouldn't grow new ones! This was because the tree was on my window seal above a radiator! " I'm stupid I know"

Anyway, I moved the tree and it started growing new shoots which was great! However, the old branches seem completely dead as new leaves are not growing on them what so ever! So now I have a dead bonsai from the old branches and loads of leaves from the new shoots! I don't want to prune it as I'll be left with no leaves what so ever? Is there anything I can do? Or is it dying? I have included pictures. Your help is much Appreciated! Thanks! Nick

It's not dying.
The branches that are brittle and dry are probably dead.
Never put a tree over a heating system.

So do you suggest i prune all of those dead branches?

Does not look dead to me at all. Leaves look greenish and in good shape. Just needs good cut back.

Once winter is over, move it outside and let it settle in for a few weeks. You should have lots of growth. Then once it is growing nice all over, trim back to the outline you want (And/or the branch structure you are after). Take the plant to a shady spot after trimming to avoid sunburn and watch the buds pop. All the old branches that then do not grow new buds, are dead and can be removed.

Tree is looking healthy now, and should not have any trouble with this treatment