If you are indeed following the "clean install" guide, then you have one of a few possible issues (or more, but these are the most common):
1. It is possible that the USB device and the BIOS / chipset aren't playing nicely. I've got a few USB keys (PNY, Kingston, some others) that just will not install a Windows OS properly on some hardware, whereas my cheapo USB2 8GB Sandisk Cruzer has had zero problems on any machine I've ever tried.
2. You have a system running UEFI, but you are booting from a non-FAT32 USB device. You *cannot* use an NTFS-formatted USB device to install Windows on a UEFI-enabled system.
3. The hard disk could have been created as an MBR disk, but UEFI installation requires a GPT-type hard disk to boot Windows from.
4. You have existing partitions on the disk, and are trying to do a UEFI installation of Windows onto a disk with less than 3 partitions (which may also need to be formatted before use).
5. You are attempting to install a 32bit/x86 version of Windows, and UEFI requires a 64bit/x64 installation of Windows.
A proper UEFI install creates 3 partitions, all of which are required - the UEFI/recovery partition, the UEFI/Boot partition, and the Windows partition. If you don't have these precreated, you need to let Windows create them during install. You may need to boot into your Windows installation USB, press F8 or F10 (or Shift+F8 or Shift+F10) at the "Install Now" window to get a command prompt window, and
run diskpart, select the hard disk, and run clean against it before attempting to install again.
If after using diskpart to clean the drive you still see a partition when attempting to set up Windows, then it's likely the protected recovery partition and a deeper nuke can sometimes be required to make it go away. Diskpart clean should be sufficient in most cases, though.