I know this is an old thread but I thought I would join up in case anyone else want's to know how to get around this issue. It's nothing to do with the install being corrupt, it's due to certain Dell laptops not allowing USB devices to boot from the USB 2.0 port.
This is the issue I had, just so that you know if this will solve your issue or not. Dell Vostro 3750, 3 USB ports in total, 2 are USB 3.0 and 1 is USB 2.0. If I attached my USB device to the USB 2.0 port it wasn't recognised during the post/boot, the USB 3.0 ports were recognised during the post/boot. With the USB device in one of the USB 3.0 ports I would get to the beginning steps of the install and an error would come up asking for a driver to be installed. The driver that is being asked for is actually for the USB 3.0 ports as they are not recognised by the Windows install.
Solution:
I downloaded the USB 3.0 drivers for the Dell Vostro 3750 (may be different for yours)
Extracted the driver to a second USB stick
Plugged the USB stick into the USB 2.0 Port (works in the windows setup, as described it just doesn't work in the boot)
Browsed to the X86 folder of the extracted files
Installed the driver a few times
Hey presto.... worked a treat.
The issue stems from the Dell bios. Whether there has been an update or not I have no idea, but not being able to boot from the USB 2.0 port is just silly.
Hope this helps