I have the same problem someone described last February. I bought my computer from MicroCenter, and they installed ESET while making another upgrade I purchased the day I bought the computer. There was a problem which required them the next day to refresh the original HP image and they installed ESET again. When I got home, it said the product was not activated, and would not take the User Key because "jt had been used too many times" or the like. I hadn't installed the program, nor received a user name and password. The program had all of my information when I tried to install with the key.
I went twice to the page at which you could give your email to get your user name and password, but I have received no reply from ESET. I hope that a moderator can help the way one helped the guy back in February on this forum with the same problem.