Hi,
It's not a good idea to downgrade the machine from Windows 8.1 to Windows 7. I don't know why users have to do this hard way: going backward. Windows 8.1 is much, much, much better than Windows 7. Anyway if you wish to stick with Windows 7, please suppy hardware id's for missing devices. The following link will show you how to get hardware-id:
http://www.wikihow.com/Find-Hardware-ID
Regards.