Why has my dog started crying at night and restless wanting out all of the time.She is not like this during the day.

Is she possible pregnant? Look for holes in the yard, if she is digging a big hole that's probably it. Something outside could be grabbing her attention (an animal most likely.) Or perhaps she is scared of something, when my dogs hear fireworks they go bookin and scratchin and all that. But other than that I got no clue

Hearing something makes sense to me.
Any rodents in the roof or walls? They usually only come out at night.

Another option is wanting to go out to the toilet, 8 years isn't old but it is possible your dog could be having some bladder problems or even a UTI.

Are they spayed or neutered?

When was the last time they went to the vet for a physical?