My taskbar won't appear when I log in!

I have a Dell Inspiron 6400 that won't bring me to my desktop.  It boots normally, presents the login dialogue window, accepts the userid and password, does the Windows "Chime", shows the desktop wallpaper and stops.  No icons, no Start button, no taskbar.
If I press CTRL-Alt-Del, then choose Task Manager --> Applications --> New Task, then type "Desktop" ... Voila!  My desktop immediately appears.  And everything works normally.
But it registers an error:
"Windows cannot find '/idlist,:4040,C:\Documents'.  Make sure you typed the name correctly, and then try again.  To search for a file, click the Start button, and then click Search."
If I then log off, it says "Saving your setting" (like normal) and produces the Log On dialogue window, like normal.  If I now try to log on, it accepts my password, then says "Logging Off" ... and eventually logs off.
If I  try logging on as a different user, e.g. "Administrator", it says "Saving your settings", then "Logging Off" (for a long time, like 5 minutes) then it goes back to the log on dialogue.
The only way to get my machine functioning again is to completely shut it down, reboot, then do the CTRL-Alt-Del --> Task Manager --> Applications --> New Task --> Desktop trick again.
Any clues?
Thanks