Hi Helen,
Norton should give you the filepath of the virus. If it's in..
C:\_Restore\
or
C:\System Volume Information\
..then you need to disable System Restore, (See
here for XP, or
here for ME, if you need advice on how to do this) run your
updated Norton, then set a new restore point.
If it isn't one of the above filepaths, then please download 'Hijack This!' from
here, unzip, and place it in it’s own folder, (not in the temp folder, or on the desktop) doubleclick HijackThis.exe, and hit "Scan". When the scan is finished, click "Save Log", and copy and paste it in a reply.
This will give us a rundown of what’s going on in your PC. One of us here will be glad to analyse it for you.
Don’t fix anything yourself yet, as a lot of the stuff on that list will be harmless or required.
Cheers
Liam