I did some changes in user preferences, but I forgot that changes and where I did them. How to I get back the initial blender settings?
In a 3D ViewPort, press Spacebar, then enter 'load factory'. You'll see an operator called 'load factory settings'.
When you execute that, you get the Default Scene back, and the settings as well. Remember to save your user settings now by going to the User Preferences, and hit 'Save User Settings', as well as hitting Ctrl + U in the 3D Viewport and save the startup file.