Screen Saver Does Not Come On

RE: Windows Vista Home Premium on a Toshiba Laptop

The screen saver does not come on, and the hard drive always seems to be
doing something, other than sitting there quietly when I'm not doing
anything. Could there be something running in the background that keeps the
hard drive busy and thereby not allowing the screen saver to come on?

I know of MSCONFIG to see what starts up, but is there a system utility that
can tell me what's up and running that may be causing the hard drive to keep
working away?

Thanks