RE: Windows 7 key
If the sticker is for Windows 8 then it should not have Windows 7 preinstalled... It makes sense that you get a non-genuine install.
The only scenario possible is Windows 8.1 Pro with downgrade rights to Windows 7 Pro. The Pro edition is rarely preinstalled on an Inspiron which is a home model.
Tech Enthusiast and Author of the Unofficial Dell Windows Reinstallation Guide