Delete following folders if present
C:\Program Files\Symantec
C:\Program Files\Symantec AntiVirus
C:\Program Files\Common Files\Symantec Shared
C:\Documents and Settings\All Users\Application Data\Symantec
Also delete following reg keys
HKLM\Software\symantec
HKCU\Software\symantec
Install SEP RU6 and try..