I had turf layed over existing lawn and now most of the gr is dead!?

The gardner did the job improperly. I would try the things mentioned by other people, but would also put a construction lien on his company (if he is still in business) as that was half-@ed at best. Lazy bum, I hope he at least charged you very little because most of labor costs ociated with having a lawn sod is removal of existing turf and laying down of appropriate top soil. And there was something wrong with the soil or the first lawn wouldn't have needed replacement. If you have any proof that the lawn was laid over the existing turf, take him to court. How quickly was it lain? Because it would of taken at least a day to properly remove old turf and add new soil. did he charge you for removal.