im guessing you're having the problem that it wont completely uninstall from the computer and so u cant put new software on there. if thats the case search google for Norton removal tool. one of the first links will be the tool on the companys website, download and run it and it will remove all remaining traces of the program. hope this helps.
Note: this is a common problem that i've found with a few antivirus's (Norton, Mcafee and Kaspersky) and they all have removal tools avaliable.