NAV has disappeared – RPC Server busy

Some of our Windows 2000 workstations have within the last 24 hours lost their Norton Antivirus, Printers, double images are being produced. When you look at Internet Explorer (Help-About) it doesn’t show to be there but you can access internet explorer. We ran online scans on these computers this morning and 0 viruses found. Please help if you have heard of anything like this?