From Help and Support:
Using Personalized Menus with the Classic Start menu
Personalized Menus simplifies the Programs menu by hiding items you haven't
used recently, while keeping all of your programs easily accessible.
You can still gain access to hidden programs by clicking Start, pointing to
Programs, and then clicking the down arrow at the bottom of the menu.
To turn on Personalized Menus
1.. Right-click the Start button, and then click Properties.
2.. On the Start Menu tab, click Classic Start menu, and then click
Customize.
3.. Under Advanced Start menu options, select the Use personalized menus
check box.