Not Able to Access Public Folders through Outlook

Hi, I am having a problem with my Exchange server. I had a group calendar in the Public Folders on my server and then it just “disappeared” over the weekend.
I’ve researched and researched, but I can’t quite figure out what happened. I can create Public Folders in System Manager, but I can’t access them at all from Outlook. I get an error message that says unable to expand the folders, the attempt to logon to the Exchange Server has failed; as well as Microsoft Outlook could not access the specified folder location, Try Again.
I realize that something is missing to establish the connection to the area where the Public Folders are stored, but I am not familiar enough with Exchange to know what that is. I want to try to reinstall Exchange, but I have been warned that it will cause Active Directory problems?
Any Suggestions?