Just to add another option to making your USB bootable, you can do it all with native Windows functions (except for XP, or mounting an ISO pre-Windows 8). I wrote this up a couple years ago, but I still use it so nothing major has changed. If you're copying the files from a physical disc, just replace the portion where I mention mounting the ISO. Hopefully my instructions make sense.
Code:
From Windows 8 / 7 / Vista:
Open CMD prompt:
diskpart
list disk
select disk x
(where x = disk number of thumb drive from "list disk" output)
clean
create partition primary
select partition 1
active
format quick fs=fat32
assign
exit
**Mount ISO (WinCDemu or other tool if not in Windows 8)**
xcopy x:\*.* /e/f y:
(x = mounted iso drive letter, y = thumb drive letter)
From XP:
Open Device Manager:
Under Disk drives, find your thumb drive. Right click > Properties. Under Policies tab, Select Optimize for performance.
Format drive as NTFS
Open CMD Prompt:
bootsect /nt60 y:
xcopy x:\*.* /e/f y:
Hopefully you're not doing this from an XP machine, but if you are just note that bootsect will have to be downloaded since it is not native to XP.