I have a multi use three year subscription to Norton 360 software. I have tried all day to add another computer. When i finally found the proper screen. I had to use the Product Key Number to activate the Next button. The site states the PSN was sent on my subscription confirmation. I used the only number which was the Product Serial Number, but it would not activate the next button. The only option was a trial offer to buy another package, which I should not be required to do. I've called the customer service center 3 times but could not reach anyone. I am hard pressed to know how this company justifies terrible CS.