While you are in safe mode, it's always a good idea to delete the content of some common areas where viruses/threats might be residing. You can do it by entering the following commands in command line:
1) Delete the content of Symantec Quarantaine with the following command:
DEL /F /S /Q "C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Endpoint Protection\Quarantine"
RD /S /Q "C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Endpoint Protection\Quarantine"
2) Delete temp files with the following command:
DEL /F /Q "C:\Documents and Settings\<username>\Local Settings\Temp"
DEL /F /Q C:\temp
DEL /F /Q C:\WINDOWS\Temp
3) Delete Symantec temp files with the following command:
DEL /F /Q "C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Endpoint Protection\xfer_tmp\"
DEL /F /Q "C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Endpoint Protection\xfer\"
4) Recreate Symantec Quarantine:
MD "C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Endpoint Protection\Quarantine"