what’s it O about ?

A bizzare thing has started happening in my File > Open dialog box in Excel 2002, when I click to open a file, instead of having the word “Open” in the top left of the panel all that’s there is a capital O. files open okay but when I try to update links to macros in worksheets and click on the “change source” when the open dialog box appears all shortcut icons are disabled and up and down level changers. Has anyone else had this problem ? Thanks for help in advance