The visual" tab in WP does not work.

I have one site, out of about 6 on the same browser platform, that has this issue: when editing a post or page the “visual” tab does not work. I can only enter a post via the html tab!!. Old posts in the site suggest a setting in my user/profile/enable visual edit tab may not be checked . however I have no such box to check…perhaps that “feature” was discontinued?

I need help with this please.