When searching for help on this topic, the jargon is "keyboard shortcuts."

The keyboard shortcuts you are referring to are built into Word rather than being something you would have added.

It is likely that some Add-In or something in Windows is causing the problem. Try starting Word in Safe Mode. That will be without Add-Ins and with a fresh normal.dot. If the problem still exists at that time, some other program is cutting off those shortcuts. If the problem does not exist is safe mode, chances are the problem is with an Add-In. There are Add-Ins that block you from saving changes to normal.dot as well.

How to find out whether any Word Add-ins have been installed
Add-ins are often installed, without asking you, when you install other programs. They are intended to make that program work better with Word. You can uninstall them and should if they don't help you.