error

I have bought my laptop from a store a couple months ago. I use it all the time to get on the internet, but yesterday when I tried to, it had said I was being attacked from a virus. I then went to download my Norton Anti Virus cd when an error messaged popped up and said that I already had Nortan Internet Security already installed in the computer. It tells me to install the latest Nortan Internet Security, but when I do that another error message pops up and says, "Windows cannot access the specified devise, path, or file. You may not have the appropriate permissions to access them." What do I do??

 

thanks!!