After lot of feed backs and requests from users Microsoft integrated the Start Button in Windows 8.1. For some users it is useful and for some people the start button not much useful. If you are second kind of person and want to disable the Start Button ironically there is no option to disable it.
However you can remove or completly disable the Windows start button in 8.1 with Taskbar Tweaker. After installing the app you can easily tweak the Windows 8.1 start button. 7+ Taskbar Tweaker allows you to configure various aspects of the Windows taskbar. This 7+ Taskbar tweaker works on both Windows 7, 8 and 8.1.