Dimitar_mar2 if you are being prompted for a qualifying product then it would appear you have purchased an upgrade. Please enter your previous full version serial number. You can find information on how to locate the serial numbers available under your account at Find your serial number quickly - http://helpx.adobe.com/x-productkb/global/find-serial-number.html.
I am seeing exactly the same issue. I have "FlashBuilder 4.6 Standard Edition" installed on my computer and have been using it for over two years. I purchased the upgrade to "4.7 Standard Edition" but it will not let me install. I enter the serial number associated with the upgrade I purchased on 7/23/14. I then receive a message saying "Serial Number you provided is valid, but a qualifying product could not be found on this computer." I am given a way to select the qualifying product I already own so I use the drop down menu to select "Adobe Flash Builder 4 Standard" and enter the serial number that I get from my adobe account's "order history" page. My order history shows "Adobe Flash Builder 4.5 Standard Edition US$249.00 Full, Mac/Win, English, Download" and a serial number. I enter that serial number and get a message saying "That serial number is not for a qualifying product. Please try another". It seems like this should just work.
So... there is a link to "Customer Support" in that same dialog, but that leads to a general support page that eventually led me to this page. I'm stumped. What should I do?
Moving this discussion to the Installing and Activating Flash Builder forum.
Jps_xyzzy you may want to review Installing and Activating Flash Builder forum to see if there is related discussion to upgrading your Flash Build 4.5 to 4.7.