Did you get any errors about the profile not being able to be loaded? Did you reboot since this happened and same thing? Right-click on the taskbar, click Customize and select to restore defaults at the bottom. Do the same thing for the Start Menu tab, click Customize and select to restore defaults.
If you don't see any programs on your Start menu, it can happen if the profile gets corrupt, does not load properly, or a virus changes things to hidden or changes user rights.