Pages Icon Button in Left Column Disappeared

I have Adobe Acrobat Pro v. 8.1.3

In the left column, there is the Pages button icon, which when clicked, allows you to see the numerous pages in your document in thumbnail format. It seems after a recent online maintenance upgrade, the Pages button icon has disappeared! I have been told by a friend that my application must be corrupted and that I should reinstall the program, which I really don't want to do.

There must be a way to get it back without a full reinstall.

Anyone have a suggestion?

Thanks