If it used to work and is now failing, then try a repair of office. If that fails to help try an uninstall/reinstall of office. Deleting the normal.dot file used to help with previous versions, but I don’t know if that helps in 2007.
This Microsoft TechNet page discusses using group policies and other methods to disable various shortcut keys. You could check in these areas and see if they have been disabled, and if so use these setting to enable them. Note at the bottom there is a link that allows you to download the information in a book format.
You can always change those keyboard shortcuts. Click on the Microsoft logo in the upper left hand of the document, it opens a menu, in the lower poertion is something called Word Options. Another window opens click on Customize, at the bottom of that window is Keyboard shortcuts. You can select how you want the shortcuts to work and you can select different keys. Thsi may eleiminate your problem, if you have 2 diffeent versions of a Microsoft Application opened.