If all else fails, I would take it down to one of the computer stores (Best Buy, Office Depot, TigerDirect, etc), explain the problem and pay them to install it.
This will accomplish two things. The most obvious is it will get FTM on your computer.
Two: There is some thing that is causing the problem in your software. What ever it is it could cause problems with your computer for as long as you own it, so it is best to get it fixed now.
With everything you have tried, I would take it down to the place where you bought the computer and present it to them as a problem with the computer, not a problem with the software. (Since it has been installed on thousands of computers, the software is OK)
I would suspect there is a problem with permissions in the OS, and it may need a hands on look by the shop.
---Have you installed other programs, using the CD drive?
---Have you checked the disk to see if there are any FTM folders on the disk? There should be a folder Family Tree Maker 2014 in the folder Program files (x86). There should also be a folder Family Tree Maker in AppData. There should be a folder in Documents called Family Tree Maker.
---Finally have you checked to see if it appears in the Control Panel, Programs, Uninstall Programs? (This is basically the old Add/Delete Programs)
Depending on what you find, this could be an indication of where the programs is ending.
(And finally, while I know this can happen, I have no idea of exactly how to correct it) The first time the program attempted to install, the install got far enough to change the OS to say it was installed. Now when you try to install it the OS see thinks the program is installed and stops the NEW installation. I believe this means something has to be added/deleted/changed in the Regeristry, OR the addition or change of a file or folder.
It it were me, and FTM was not showing in the Control Panel Programs, I would consider deleting all folders that I mentioned above for Family Tree Maker.
If It was showing in the Control Panel Programs, I would try to delete it from there.
Please remember I do not always know what I am doing when I work with my computer's OS