Explore.exe locks processor on boot.

Upon bootup, the explore.exe process uses 100% of the processor, as seen in the performance tab of task manager. Upon killing the process with End Process Tree, usage drops to 0 to 16%. But now, Norton Antivirus must be re-enabled for email otherwise Outlook-XP will not connect to server. Why is the Explorer.exe using 100% and why won’t the enail antivirus remain enabled?