Can not access worksheet unprotect in an Excel worksheet that I have been using for several weeks

I have a worksheet I created and have used for several weeks.  It has several Macros and many of the cells are protected.  Now it is not working correctly.  It can be opened and the unprotected cells are available. However, the sheet can not be unprotected. Unprotect buttons are visible but are greyed out and not accessible. Most of the Macros do some sorting of data and will not run, I assume, because of the locked cells. This problem involves only this worksheet.  The other workbooks and sheets work fine and I can create new sheets with Macros and protect and unprotect  the new sheets.