crash desktop enviroment

When I have activated screensaver, the system doesn't give back the password's pop-up, the screen remains black, but the application are running, I have shutdown the PC from start button and after restarting it has given me following message:
“There was an error starting the GNOME Setting Daemon,
Some thing, such as themes, sounds, or background settings
may not work correctly.
The last error message was:
Did not receive a reply. Possible causes include: the remote
applications did not send a reply., the message bus security
policy blocked the reply, the reply timeout expired, or the
network connection was broken.
GNOME will still try to restart the Settings Deamon next time you log in.”

I don't restore my desktop and the system starts slowly and with more difficulty. Anyone would help me!!!
PS: Excuse me,my English is poor.

Thanks in advance.
Pietro