I had some troubles with my UI(like windows classic), can someone help me?
Have you taken any action with themes, or uninstalled any items?– Lewis Goddard ♦Nov 17, 2015 at 18:49
I am not sure of why it could happens, but try the following :
Install Gnome Tweak Tools
sudo apt-get install gnome-tweak-tool
Then launch it :
And make sure that everything in Appearance is set to elementary