well you have two choices here.
1. you can goto websites like http://www.tucows.com and http://www.sarc.com and download the virus patterns manually. This is for free. Eventhough your antivirus free virus pattern upgrade period is over you can still get it free from here.
2. you can go buy any pirated version and get it free for another year.
BUT...if your computer is already kinda slow and outdated i suggest you do (1) because newer versions of antivirus basically eat more hard disk space and more memory, yes they look better but do the exact same thing but its alot slower if you got a slow computer. :lol: