My dog has not wanted to drink or eat water he has slept and hidden from us the past few days and when I tride to put food in his mouth I noticed that his mouth was cold and drying out I really don't know what is wrong.

I think you should take him to the vets because as he's quite young still they noramlly tend to eat anything they find, don't worry too much if you take him vets I'm sure they will find out what's wrong, if you want in the mean time try and make him at least drink water because that's quite important x :D hope this helped

It sounds like it's time to visit the doggy doc-doc. Please take him to a vet.

Sounds like Parvovirus. Be sure to keep him hydrated and take him to the vet.

At 7 months it could be that he is in pain from teething and simply doesn't want to eat because he knows it's going to hurt.

Are there any other symptoms other than lack of desire to eat and hiding when you offer food? If he is not drinking I would give some pedialye to get his hydration levels back up. Dehydration is a dangerous spiral, the dog doesn't drink, then feels sick so doesn't eat and in turn doesn't want to drink again.