If you put a hand into the top of the fern, you should feel several hard 'knuckles' and these will be the new fronds ready to uncurl
If you don't feel any hard bits, and it is all soft, then they may be dead.
But most tree ferns have two flushes of new fronds - one spring time, and another mid summer.
Move your fern to shade, and keep watering it once a day or twice a day in hot, dry weather, and see what happens later in the year. And feed once a week - they love Tomorite or other tomato food, or sea-weed based food. Basically keep the crown damp and shaded, and this may promote some action
What variety are they? Dicksonia Antartica are hardy, but young or exposed trunks should have a ball of hay in the crown to protect from frost.
If you have any other variety of tree fern, then they are not generally UK hardy, and should be sheltered over winter.