Antivirus 2011

Norton came with my Fujitsu computer.  When the first year user agreement ran out I attempted to purchase and install Norton Antivirus.  It didn't work.  I ran the uninstall program downloaded from the website but the program still won't install.  The message that comes up is that another installation program is running.  Any ideas.  I had the same problem before attempting to install the new program also.  It wouldn't update from the website.  Any ideas