There are so many priors that I'll answer why it didn't work for you. The supported dual Windows install is from oldest to newest. Do that instead and when you start with a blank HDD be sure to leave unpartitioned space for the next OS.
As to the app that won't install, my method is to fix that rather than spend weeks on OS tinkering.
I am Ashish Dewan. I am new to this online discussion board. I need some help from your side. I want to install Dual OS. Presently, I am using Windows 8.1 & now I want to install Windows 7 as well. The reason is behind doing this is I am unable to install some software through Windows 8.1. Kindly instruct me how I will be able to do this. I want to know its merits and demerits as well & if possible kindly suggest better Antivirus which provides free service to protect my PC against virus attacks. I am waiting for your responses.