If the current grass is actually dead and not just dormant then the dead grass will not come back to life.
If the grass is truly dead then you'll need to break up the soil and replant new grass seed to get new green grass growing where the dead grass was.
Best thing to do is till up the yard and remove the dead grass and then apply new grass seed and fertilize and water the new grass seed and after a period of time you should see new green grass grow in it's place.