Can't open door...Help

Well if you have the door card off, you can now have a basic understanding how the things work. Get a helper and a good light and look into latch area, pull up and down on the door lock knob that operates the latch, where does it attach. Have a helper push the button on the door handle what does it do...take your door key, operate the lock does it go full cycle. I have seen the cylinder lock arm loose, causing a lock position no matter how you turn the key. And try the inside door handle is it binding does reach its full travel? I have had someone push on the outside of the door while trying the above and it seemed to let pressure off the latch. There are areas on the latch you can push and pull to make it operate without using the door handles......