Uninstall and Reinstall Norton AV might fix this. Then perform definition updates. If this is the Norton that came with the system new and you have not paid for an extension to the protection through symantec, then it may have disabled protection, however I have only had where Norton's Definition Updates Expire and it continues to run on old definitions and reminds me over and over again to pay to update. I have since uninstalled Norton from all my systems and I run Microsoft Security Essentials which is free from microsoft. Have been using that for over 3 years now with no infections and no problems.
