I am following MaG walkthrough and have completed all the tasks thus far. I have just opened the poster display box and looked at the back of the poster. When I call Melina she just tells me she is busy and cannot talk now. She does not give me the password for the authentication database. I am stuck and cannot go any further. I don't know know what I am missing. I have followed everything in the walkthrough and not had any trouble completing any tasks. I even went back and redid the portion in the underworld prior to this part. Any idea what I may be missing? I am really stuck and don't know what to do. Any help will be appreciated.

Do you have any incomplete tasks (are you going the amateur mode, or Master?)

Also, did you try conversing with all characters (around the place and via phone?)

I am doing amateur mode. The incomplete tasks I have are:

1- Password for authentication database
2- Find a way to cross river of fire
3- Trigger keypad in Tartarus
4- Figure out what's inside 3 judges trunk
5- Create temple designs

I have talked to Niobe several times until she doesn't have anything else to say.
I have talked to Thanos a couple of times when getting the rubbings on the plaques.
Every time I try to call Melina now all I get is her voicemail.
I called Frank and Joe and talked to them and called Melina again and only got voicemail.

Can you tell if I need to talk to someone else or do something else?

You can create the temple designs now. There is a piece of paper that is lying on one of the benches in the center of the museum that will enable you to do this puzzle. It's not far from the temple display - turn around from there, and it is in that general vicinity.

The walkthrough states:

Thanks so much. I had done the first temple, but didn't realize I needed to do all 3. After finishing all of them I was able to talk to Melina and get the password. You really saved me. I was going crazy. LOL

Glad to help! Have fun with the rest of the game.