If you want to open the Command Prompt window on your Login screen or the Boot screen in Windows, here are different ways to do it.

The Startup Settings boot menu allows you to change various settings that affect how Windows 8 starts up as well as providing a launching point into Windows 8 Safe Mode. To access the Startup ...

Detailed information about the various settings can be found here: How to use the Startup Settings boot menu in Windows 8 To select one of these options simply left-click on them with your mouse.