Surface USB/PXE
This process is for a Surface Pro 2 device
Step One
Disable secure boot by booting the device while holding the volume up button, and release the power button when the Surface logo appears.
Step Two
Insert a bootable USB or USB to ethernet adapter. If you are using an ethernet adapter you must boot into the os first (if possible) or at least attempt to boot with the ethernet adapter plugged in to allow for driver initialization.
Then boot the Surface by holding the power button and volume down and it will boot into the USB or PXE device.
The Setup USB
The setup USB is not a normal Windows 8.1 install USB, and will boot into a blue screen that gives you different options. If you wish to "reinstall" Windows on a Surface, you must choose troubleshoot and reset device.
Other Surface Related Links
This process is for a Surface Pro 3 device
Step One
Download the image and set up the bootable USB [1]
Step Two
Use the drive to restore the surface [2] https://support.microsoft.com/en-us/surfacerecoveryimage