I saw a post somewhere else that this issue is due to usage of USB 3.0 port when installing OS with a flash drive. I plugged in the USB key into the USB 2.0 por and that resolved the issue. Hope this helps your problem!
Hi,   I  purchased and installed a SSD in my Dell Vostro v131 and when I tried to install windows 7 using a USB key, i get the message below and cannot continue the installation. A required CD/DVD drive device driver is missing.  If you have a driver floppy disk, CD, DVD, or USB flash drive, please insert it now.  Note: If the Windows installation media is in the CD/DVD drive, you can safely remove it for this step I created the bootable usb by following these instructions: 1. In Windows Vista or Windows 7, open an elevated command prompt and run the following commands one by one: a)   Diskpart b)   list disk You can identify your USB drive by its size. For example, it is disk 1. c)   select disk 1       Select your USB drive. d)   clean      Clear it. e)   create partition primary f)   select partition 1 g)   active         Mark this partition as an active boot partition. This will enable this USB drive bootable. h)   format fs=ntfs quick 2. After formatting the USB drive, copy all the files in the DVD to the USB drive   I copied the contents from the OS DVD that came with the v131 when I purchased it. Win 7 Home Premium SP1 64-bit i've installed Win 7 on my desktop following the same procedure and i have never seen this message before.. Can anyone shed some light on this problem?? Thanks in advance!  
error message when trying to install win 7 on vostro v131