Please, I really need someones help, QUICK?

Ok, a year ago I purchased Norton 360 on disk. And it says a year protection for up to 3 pc's. I used the product key for the first year and that year has just ran out. Now I still have Norton 360 on my computer but it has "expired" and I am not protected. My product key has now been used up so I can't use that again, but I thought it said for 3 pc's? Can't I just use it twice more on the same pc? Please help. What do I have to do? Thanks.