I'm trying to install my purchassed Lightroom 5 to my laptop. It was installed on my PC about a year ago. I tried 3 times by following the Download instructions but whenit gets to the stage where the serial number is displayed in the download center

I'm trying to install my purchased Lightroom 5 to my laptop. It was installed on my PC about a year ago. I tried 3 times by following the Download instructions but when it gets to the stage where the serial number is displayed in the download center it shows no download. I was assured when I purchased the program that I would be able to install it on my laptop when I needed to travel with it. I will be leaving in three days and NEED to get it on my laptop NOW. Please help. I am not very computer literate so need simple instructions please.