Help me - what simple thing did I mess up?

[Mr Curious]

What did I do? When I click on the Finder on the dock (blue / white face) I get a new Finder window with no Sidebar. I have the Sidebar enabled in the Preferences.

But when I double click on the Icon for the start up HD I get the regular Finder WITH Sidebar.

How do I keep this turned on? Thanks for a solution.