changing my 2010Norton for a new 2011 cd installation, problems

Hi, can anyone help me please. I have Norton 2010 installed with XP (a cd I bought and installed myself, worked fine) now I have bought a Norton 2011 CD to install as 2010 will run out soon. Have done the installation and even cleaned pc but when I put the 2011 cd in it will not take me to putting the key number of the new one in. When my pc restarts it does have Norton on but it tells me that it only has 11 days to go - which of course is my old 2010 Norton. Any easy to understand help would be appreciated, thanks