Compatible products for windows vista basic

Hi

 

My current norton 2011 internet security expires in 4 days and i purchased the 2012 version off ebay.When i tried to install,it stated not compatible with my system.Im not savvy with computers and in the past,the nortons i have purchased have installed no problem,i have used cd's in the past and this one came via email,do i have to remove the current norton or wait for it to expire before i can install another.Please help me to get the right product to install as im running out of time.Thanks.