I have had a surface pro for a while now and I have decided to try and boot from USB on it.
It won't boot from it.
I have tried an external hardrive with Windows Vista on, a Windows 98 Microsoft-dos boot disk and even a Windows repair disk on an external disk drive. All of these devices boot on everyone of my computers except my surface.
I have tried disabling secure boot keys in the BIOS and I have tried booting via Windows 8 advances options and by holding down the bottom volume rocker at start up. None of it works.
Best Answer
http://blogs.technet.com/b/askcore/archive/2013/03/20/creating-bootable-usb-drive-for-uefi-computers.aspx
Note Surface Pro only supports 64bit windows, so it's possible only a 64bit windows repair disk will work. Note the Windows USB/DVD Download Tool formats the drive with NTFS, instead use Rufus so you can format the drive with FAT32.