Here's how you can boot to the Windows 8.1 desktop instead of the Start screen.
1. Go to the Start screen.
2. Type "taskbar" without the quotes.
3. Choose Taskbar and Navigation.
4. A dialog box will appear.
5. Choose the Navigation tab.
6. Click the option for "When I sign in or close all apps on a screen, go to the desktop instead of Start."
7. Click the OK button.