How can i prevent my hedge from dying?

Hmmm... looks like a privet. I suspect it's past its sell-by date, I'm afraid. It really doesn't look happy and I don't think the dead wood will shoot again. Sorry.

I think you may have to start again. :-(

If you're not too keen on starting again, you could try cutting it back into shape (back to where the dead is all along), and give it a liquid feed and make sure it's kept well watered.But first, you might want to investigate the "dead" patches - see if the branches snap off (that means they're definitely dead) or whether there's any life left in them - if you can't snap them, scrape a bit of the bark off, see what colour it is - if its moist underneath and doesn't just snap, that bit isn't dead.

I agree with Spritz.