IIS7 re-installation failed due to HTTP service disabled

Symptom Customer complained that he tried to re-install IIS7 as he found WWW service couldn't be started. However, the installation always failed and was reported "fatal error during installation". Based on our experience, we uninstalled WAS (Windows Process Activation Service) first, and then tried to install IIS7 again. Unfortunately, we still got the same result.  IIS7 installation log looked