The Windows 8.1 x64 and x86 Enterprise .iso can be downloaded from here:
Once you register you will get a product key for a 90 day trial.
Creating the Bootable USB
You may use Rufus to create a bootable USB:
Rufus does not need to be installed and can be run directly by double clicking on the application.
Select your 8 GB or superior USB flash drive:
Select the .iso:
There are two types of bootable USB you can make with Rufus The “GPT partition scheme for UEFI computer" or the “MBR Partition Scheme for BIOS or UEFI Computers".
Globally Unique Identifier Partition Table (GPT) Partition Scheme for UEFI Computer
Use with Dell hardware and Windows 8.1 64 Bit with a UEFI BIOS later than 2012. Enable UEFI and SecureBoot.
Requires systems that have a Unified Extensive Firmware Interface (UEFI) Basic Input Output (BIOS) and also 64 Bit Windows. These requirements are in general standard across hardware post 2012 i.e. hardware Dell shipped with Windows 8 or later.
This is a new partition scheme which is more reliable than the MBR partition scheme. In GPT multiple copies of partitioning and boot data are stored on the hard drive and checks they are consistent.
This partition scheme has the advantage in the fact that it can support >2 TB drives and can create up to 128 Partitions.
This will support newer security technologies such in the UEFI BIOS such as SecureBoot and these should be enabled.
2010-2011 hardware may or may not have a UEFI BIOS and you will need to check and enable the settings in the UEFI BIOS setup if applicable. These settings will also need to applied correctly for systems that have previously been running Windows 7 (e.g. downgrade rights).
Master Boot Record Partition Scheme for BIOS or UEFI Computer
Use with Dell hardware and Windows 8.1 with a Legacy BIOS earlier than 2010.
This can be used for an older system pre-2012 with a legacy Basic Input Output System (BIOS) so is required for pre-2012 hardware and for Windows 8.1 32 Bit.
Limited to 2 TB of space and to 4 partitions.
This partition scheme is less reliable as the partitioning and boot data is stored in one location meaning if its corrupt then the data is lost.
If you do not select the USB Device, then load the .iso and then select the Partition Scheme and File System in order, Rufus may revert some of the settings to defaults which may be incorrect.
Select the “GPT partition scheme for UEFI computer" or the “MBR Partition Scheme for BIOS or UEFI Computers" respectively depending if your hardware is post 2012 or pre 2012.
Select the FAT32 file system. SecureBoot requires the bootable USB to be formatted as FAT32 otherwise it won’t boot.
Select OK to format the USB flash drive:
Rufus will now create the Bootable USB:
When its ready it’ll say “Done" to the bottom left. You may now close Rufus and have a bootable USB for installation.