It sounds like you have an add-in that is blocking changes

Go to Tools/Templates and Add-ins and see what else is loading with Word and list them here. Adobe (not the reader), Norton, and Winfax are programs known to block changes.

You also need to check for COM add-ins that do not appear in the add-ins dialog box:

1. On the Tools menu, click Customize.
2. On the Commands tab in the Customize dialog box, click to select Tools.
3. In the Commands list, click to select the COM Add-Ins command, and then drag the COM Add-Ins command to a toolbar.
4. In the Customize dialog box, click Close.
5. Click the COM Add-Ins toolbar button that you added above.

In the COM Add-Ins dialog box, the add-ins that are available (loaded) in Microsoft Word are listed. To temporarily turn off a COM add-in, click to clear the COM Add-In check box, and then click OK. When you restart Microsoft Word, Word will start without loading the COM add-in.

To remove the button you added to the toolbar, press Alt, hold down the left mouse button and drag the icon down to the document window (or reopen the Customize dialog box and drag the icon from the toolbar). This will generate the prompt when you shut Word down, answer yes.