Norton Anti-Virus

I receive a message to remove another version of Norton Anti-Virus when I try to install one from system works 2003. It supposedly was uninstalled. I can’t find any files. When I boot I get a message can’t find a file then command line shows:C:\progra~1\Norton~1\navap.vxd. The in the deskop a message says symevnt/.dll and I cance. Can you help me install the new antivirus program.