"A required CD/DVD device driver is missing" upon windows 7 install

I've been trying to install Windows 7 on my Asus Q501L (which came with W8 already installed) via USB. I faced a problem - while the laptop was able to start the initials steps (the black screen where it shows the copying process of the Windows 7 files), i couldn't go any further than the step at which i need to choose a partition to install the OS on.

It simply says " A required CD/DVD device driver is missing" - when you start Windows 7 or Windows Vista from the setup disk". I tried Shift-F10 to start the CMD and format the HDD (NTFS format) on the spot, restarted, same error message. I disabled Fast Boot in the BIOS, the SATA controller is set to AHCI. I tried several topics @ Tom's Hardware forum, and elsewhere but i still cant find a definitive answer.

I read that maybe i should change the AHCI controller to IDE, only issue i face is that in BIOS i get no options - there's only AHCI as a choice, no IDE, no RAID.
Any Ideas? How do i get IDE controller option to appear in the BIOS settings (via the registry keys, or maybe i need to download that IDE controller (not sure if thats possible)) from the Intel's website (intel core i5 is the CPU of my laptop if that's of any help)?

Thank you

Thanks for the fast reply

I looked into it, i tried the ideas which i haven't tried yet and i still get the same message.
I noticed that i have CSM, no UEFI booting option.

Look at Step 4.

Make sure you are plugging the flash drive to a USB 2.0 port. If you are using a flash drive for install and DISKPART can see/delete/partition your hard drive without issues, then it is certain that Windows installer is failing to find a valid installation media ( in your case USB ) and which results in "A required CD/DVD device driver is missing" message ( the message is hard coded with DVD in mind. It won't change even if you are using a USB ).

On a laptop, Intel USB 3.0 ports can be configured in two ways.

1. Native XHCI mode.

This is the native mode of USB 3.0 like AHCI mode of SATA ports. Like WinXP requires special drivers to access AHCI ports, Win7 requires special XHCI mode drivers to access these ports. Laptops which are designed with only "Windows 8" in mind usually use this mode.

2. USB 2.0 compatible or EHCI mode.

In this mode, Windows 7 can see and access USB 3.0 ports even if you never install any special USB 3.0 drivers. But the speed will be limited to USB 2.0. If the driver is installed and a USB 3.0 device is plugged, the driver will automatically switch the port to native mode and then the port will work at full USB 3.0 speed. Laptops which are designed to install and operate either 7 or 8 are usually configure ports in this mode.

Additionally some laptops came with only USB 3.0 ports and some others came with a mixture of 2 and 3 - one or two ports will be USB 3.0 and others will be USB 2.0. If your laptop belongs to second category, simply plugging the USB flash drive to a 2.0 port will do the trick. Windows setup will see and access the disk. If all ports are USB 3.0, you may need t use a DVD for installation.