I log out of the page. when trying to go back to main page the Admin tab option is missing only Gallery tab is visible. Using firefox and internet explorer. How can I log back into admin to post more picture.

Which Zenphoto version?
Which theme?
Please try to describe exactly what you did.

If you were logged-in - then did you use the correct username/password for the master account?
Not the username/password for some other user account?

"I log out of the page" - what page?
"trying to go back to main page the Admin tab" - how/where?

Also maybe please take a look at this recent topic:
http://www.zenphoto.org/support/topic.php?id=1409475#post-1977883