Welcome to the world of Norton. You might look for an option that says to scan floppies at shut down, or simply right click on the norton icon in your system tray and disable it, then shut down. When you start back up, it should launch as normal.
Matt J.
P.S. Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.