I have a Pomeranian Doggy of 10yrs old. She has become now deaf and blind. Recently she urinates frequently inside the house. What do I do to prevent her from doing so and what could be the reason for her behaviour.

Are you seeing her urinate in the house, or you just come home to puddles?
She could be experiencing incontinence. She also may have a urinary tract infection. It's best to visit your vet to determine if it's a medical issue.
If not, then it very well may be behavioural. Has anything changed? New animals, new furniture, new people? Moved?

She goes out as well, but sometimes she if the doors are closed, she urinates inside. Vet says there is no urinary tract infection. Few months ago we purchased new furniture, but she urinates inside my aunty's house too, if she goes there.

Have there been any changes in the home? New puppy? New child? Work schedule changes?

It could be age related, but it could also be related to something new in your home. I have the same issue with my 9 year old border collie cross. He started urinating in the house when we got our new beagle puppy.

You could purchase or make a doggy diaper. Only use it when the dog is in the home, and then work on reinforcing potty training. If it is age related than retraining won't work, but the diapers will help save your furniture at least. :)