So I recently had problems installing Windows 7 SP1 with an original certified Dell installation DVD using a Samsung thin profile SE-208 external USB DVD/CD. Upon booting to the Windows 7 installation, after telling the Windows 7 installer to go ahead, it said that the DVD/CD ROM drivers were missing. I also could not install with a bootable Windows 7 USB key that I created by first ripping the Dell DVD to an ISO with IMG Burn, and then creating a bootable USB drive with rufus-2.12.exe. The same error – no drivers detected. After finding this post here, it came to me that I had only tried the external DVD drive on the USB port that is on the right-hand side of the laptop (USB 3.0). I instead connected the external USB DVD drive into the Left-hand side of the laptop USB port (USB 2.0) and booted the DVD into the installation and proceeded normally. So if this happens to you, connect your bootable device to only a USB 2.0 port, when trying to install Windows 7 on a newer PC or laptop that has both USB 2.0 and USB 3.0 ports!