I installed gnome shell but when I start it it's the design of gnome classic... what can I do? I already reinstalled it. I have Ubuntu 11.10.
This might be trivial
To make sure, install again gnome-shell from a terminal:
Log out your session or restart your computer. Now, select the Gnome-shell session at the login screen. Otherwise it will start your default session, which in this case might be classic Gnome. Check this image for reference.