There may come a time when you need to completely erase the history of
your downloaded guide data and tuner setup. Something may have gone
wrong with your setup, tuners may have changed or maybe you’re just
looking to clean house a little. Don’t worry, this isn’t going to
require a complete reinstall of Windows 7, the process is in fact quite
easy. Windows 7 Media Center stores all the information we need to clear
inside database files stored inside the ProgramData folder. However,
we’ll need to close a few background services before we’re able to clear
the files from the drive.
http://www.hack7mc.com/2009/09/clearing-guide-data-and-tuner-setup-from-windows-7-media-center.html