My dog started peeing all over the house. Now, he is peeing in the lv on my chair... what can I do??

Is there some change like another dog or something for him to be jealous over? Or are you leaving him home alone more?

Can you confine him to one room and only let him in the rest of the house for certain lengths of time? Let him know when he does this that he can't be doing it (like a light smack on the nose and tell him NO) Then confine him to a small room for awhile.
Praise him when he asks to go out.

If he is an older dog and can't help it there isn't much you can do. If he is older and can't help it I have known people to put pampers or depends on their dogs.

This could due to a number of things you didn't mention. Unless there have been some other large, obvious changes in your dog's life, the place to start is the vet's office. For any help you are going to have to give us more information.