"Too many computers authorized."

I tried logging into my books app on my laptop and received a pop-up to authorize the computer. So I went to the account menu, selected "Authorize this computer". I then received another pop-up stating that I was only allowed 5 and I had exceeded the limit. I've checked everywhere I knew to check and couldn't find anything but one other laptop. Maybe I'm looking in the wrong places? Or there's something wrong with how I'm doing it? I don't know, but I just want to read my books on my laptop and I'm too stubborn to just read them on my phone, now. If anyone knew how to help, and could lend some advice, that would be greatly appreciated.