Laptop Won't shut down, or respond to control alt delete.

My laptop is a few years old and has been working fine.  Its an inspirion 1545.  The other day i realized the toolbar at the top of my desktop was good (dell dock).  When i went to download it back, the loading screen froze.  When i tried to use control alt delete to get the loading screen to stop, there is no response from the computer.  When i go to shut down the computer, there is no response either.   My anti virus says theres no virus and dell support says the pc is working fine, but i don't know what to do! Please help me!!