Computer does not shut down

Hello,

I recently installed Windows 7 on my Dell Inspiron laptop that I purchased earlier this year. Since the installation, my computer will not shut down. It get's stuck on the logging off screen. It will stay on for days if I do not turn it off. Prior to the screen that tells me it's logging off, I get a 3 second screen that tells me that something is still running. Because the screen is soo quick, I cannot see it. I think it must be something with the internet because I noticed if I do not go on line, it seems to shut down with no problem.

In my limited computer knowledge, I attempted to force quit. When I hit control, alt, and delete...nothing appears in the task manager.

Please help....

Thanks!