Must change folders to receive new mail

Here is my problem:  

I am using MS Outlook XP to connect to my company's Exchange server.  Outlook is able to retreive all of my mail but I must change from my inbox folder to any other folder, for example, Sent Mail, then return to the inbox and if there is new mail on the server, only then will it appear in the inbox.  Even if I click on the Send/Receive button the new mail is not received.

I have Outlook configured to check for new mail every 5 minutes, but as I mentioned above, this does not work.  I keep Outlook open and minimized.  In the past, I would receive a message box stating I have new mail, would I like to check it now.  If I wait long eneough (about an hour) I do receive the message box and the mail does make its way to the inbox.  That is just too long.

I want to get outlook back to where it notifies my as soon as I receive mail and I do not have to change folders.

I tried to repair the installation of Outlook XP and that did not solve my problem.

I am running Windows 2000 Pro.

Thanks for the help!
-- Chris