Get and run the Norton removal tool
http://majorgeeks.com/Norton_Removal_Tool_SymNRT_d4749.html
The below is a good cleanup I would run it thru to clean the "File Not found" then back to top and search for Symtdi.sys then Norton then Symantec and remove them all.
Autoruns cleanup
Make sure hidden files and folders are shown. Open Windows Explorer click Tools or View and then Folder Options-View.
Choose Show hidden files and folders, uncheck Hide protected operating system files and click OK.
Download install and run AutoRuns
http://technet.microsoft.com/en-us/sysinternals/bb963902.aspx
Run it let it scan, then when it says ready at bottom left corner, make sure the EVERYTHING Tab is selected and then click File at top and then Find.
Type in the find box
file not found and hit enter and delete all lines that have file not found.
When you reach the bottom the go back to top and click the first entry under The Everything Tab (to begin the search from that point) and search again in case any were missed.
This is a bunch of old stuff that M$ thought you might or would need that no longer exist, or for computers that are assumed to have SCSI or AMD processors but do not, or that you have Intel but do not!
After the
file not found search scroll back to the top and highlight the very first entry so you are searching from the top and click Find and search for anything you want, if needed.
Then look carefully through all the Everything entries and delete anything that you may
have had but uninstalled and thought were gone. If you are sure delete these also.
Mike