If you are using Windows, check if Autoplay is disabled. Open your Windows Explorer and you will see iTwin as a CD ROM device. Open it and run iTwin.exe
To start over at any time:
- Unplug your iTwin
- Uninstall iTwin if already installed
- Log out of your account and log in with an account that has admin access
- Ensure your computer is online
- Plug in iTwin to start afresh.