I installed WordPress 2.8.5 from WordPress.org directly without upgrading.  When Writing a post, I was not able to see the buttons for the Visual tab.  I thought it might be that the Visual Editor was disabled as mentioned in many help forums, so I moseyed over to my profile only to find that I didn’t even have the check box to disable the Visual Editor available to me.  After researching further I was able to put two and two together and figured out that there were files missing from the wp-admin folder.  Actually, in my upload of this folder, many of the sub-folders didn’t transfer.  The one folder in particular that was missing and causing my Visual Editor problems was tinymce.  I don’t know if it was a problem with my broadband  internet connection (I have recently been experiencing intermittent disruption in the connection) or the ftp software I used to upload wordpress.

This post was helpful in understanding why this happened.  My problem was a little different because I installed WordPress 2.8.5 from WordPress.org directly without upgrading, but I figured out from this post that there were files missing from the wp-admin folder.

http://www.feverishthoughts.com/2009/07/06/i-fixed-my-wordpress-2-8-visual-editor-problem-sorta/