Cannot access programs in Start Menu

I have a rather strange issue with a Windows XP system. The list of programs under “All Programs” in the Start menu has disappeared when using the XP start menu. Everything works normally when I change to the Classic start menu, but when I hover the mouse over All Programs in the XP start menu, nothing happens. In addition, when clicking on Run, Search, or Help and Support in the XP start menu, rather than activating those functions, I get a message stating that a shortcut cannot be created there. These items work properly under the Classic start menu. I have updated AVG, Spybot S&D, and AdAware and scanned the system, finding nothing. Any ideas?