Trouble Installing Lightroom 5 on El Capitan

My MacBook Pro hard drive crashed and was replaced by the Apple Store with a new hard drive.  All my programs were lost (not that many, really, Lightroom 5 and Word for Mac), but at least I had previously moved all my photo files to external hard drives.  After upgrading to OS X El Capitan I tried to use my Lightroom 5 installation DVD and it seems to load just fine, but never asks me for my product code (serial number) and all I have is "LIghtroom 5.7.1" as an icon on my desktop.  When I click this icon it takes me thru the activation / installation protocol and says "installation successful" but when I click on the icon it simply starts that protocol all over again.  I've been to the chat feature 4 times now and the last agent advised me to come to this forum.

I've used the DVD only twice previously, first for the original installation on this laptop and second for home PC.  All my other attempts were to reload onto this laptop.  I'm not sure what else to do.