Temporary fix:
Go to the Symantec website and use the Intelligent Updater option (once there,
select Downloads, Virus Definition Update, Download Virus Definitions
(Intelligent Updater Only), Download Updates and then click on the .exe file
under Filename.
If you have dial-up, this will take awhile as the file is just over 8MB. You can
choose to save the file and then double-click on it to install it (I believe) or
just choose 'Open' rather than save the file and it will do it automatically.
If it works, first do a complete and thorough virus scan.
Then, if all is clear, you can work on the other problem; sometimes an uninstall
and reinstall of Norton is the quickest.
Or, go to the Symantec website and go through their online help program.