How to get 'favorites' to display in finder...? I used to have several favorites in the sidebar of the finder window, but today they are gone.  

I cannot drag folders into the sidebar, and I can't display the ones available to choose from in Finder > Preferences.  WTF?

Here's a little screen capture of it misbehaving:
The first thing to try is to make a new user account and then see if the finder sidebar functions there.

If so, you can log out and delete that user account and then make a backup of the system. You'll want to delete the user preferences for Finder.

defaults delete com.apple.Finder


Then log out and back it to see if the finder sidebar is working.