To go back, use the two arrow buttons facing left. The central message indicator lets you know how many messages you have to view. Unlike e-mail, messages can expire if you do not read them. There was a message that I was interested in last week. Now it's gone.
Messages have expiration dates.
Once they expire, they cannot be seen again. I can't find the Messenger in my taskbar. Not if you have already installed it. Check your desktop and your Start Menu for a shortcut to your Messenger. If you cannot find one, then you should probably re-install your Messenger.