Oh dear! Once a plant decides to start dying there's not much you can do. Did it get too cold or waterlogged over winter? You don't say which part of US you are in. If it was too wet, put it somewhere to dry out and hope for the best. Don't give up too soon as it may re-sprout from the base.

If you're the person who recently asked whether you'd killed your Yucca by leaving it outside, the only thing you can do is bring it in to the warm and keep your fingers crossed.