Windows Explorer Error

I have a new XP machine with a small problem. The “My Computer” & “My Documents” icons on the desktop and in the start menu for do not work. When I try and open these items I get the hourglass pointer for a couple of seconds and then nothing. When I go to restart or shut down the machine I get and End Program dialog box for explorer.exe. I have also stopped the explorer.exe from running and then started the process againd and that seems to work until I restart the computer. At that point, the proble m starts again. Any help or ideas?