can any one give me any ideas skin dry but no signs of any reason for it skin dry 

Groomers do an excellent evening primrose oil shampoo that rehydrates the skin. They have two grades available, I use the vet grade and have had great success with it. I also use their evening primrose oil supplement.

The first thing you need to address is diet

Hi, I agree with Perry - check diet first.  However it could be caused by any number of factors.  If you can give us some more information about your dog (age, general health, diet, when the problem started etc) we might be able to be more specific. :)