breaks

We just replaced the brake line on a 1994 ford aerostar van. I worked for a week and then we had no brakes. We in the end we replaced the back brakes. However we still have no brake pressure. We tried to bleed them but they wont bleed.
Im looking for any ideas of what this could be and how we can try to fix it.
Thank you for your time and help....

They should bleed unless you have a bad master cylinder. How are you trying to bleed them ?