The user that you logon to is it a member to a group that has access to edit/admin? The location path for episerver interface has some default groups. Is it only the pagetree or the complete edit admin? Open firebug and view the console for errors as well. Might get some error when trying to render the edit tree.

Yes, the user has access as admin via ws_federation. And only the pagetree seems to be failing. Some other areas may be failing as well, but I can't edit pages so far.

If you run it with f12, do you get any errors or something like that in the console?

Yes, I am seeing errors. It says,

Could not map property ContentGuid - table tblBigTable does not contain any columns that map to DbType.Guid

This might be a long shot but how did you create you db? The error could be cause of the fact you do not have all sp in right place. Not sure how you work with Ws Fedaration actually but I found this threads about a issue looking like this:

http://stackoverflow.com/questions/13233294/could-not-map-property-languagebranch-table-tblbigtable-does-not-contain-any-c

http://world.episerver.com/Modules/Forum/Pages/thread.aspx?id=60826

The version of episerver is cms 6 but it might relate to your issue as well.

Consultants initially built the site. They handed the site to me, so I don't know the details of that. Yesterday I did some research and found that the database scripts to update the table haven't been run. I am running into a similar error when running the update-epidatabase command from the Package Manager Console.

I had similar problem like you, the page tree was not showing but site was working normaly. I've did what Eric suggested and generated new scripts but htis time with different target and problem was solved.