Installing WIM file using USB

Hi,

I want to install captured image using USB. Not sure where I went wrong. here is what I did.

I captured an image(windows 8.1 x64 ) using MDT . I have used the captured image in WDS it works fine. But I wanted to use USB (as the file size is 6GB cant use DVD) to install on remote machines. 

Than I converted it to ISO. I followed a step in http://www.ehow.com/how_5750929_convert-wim-file-iso-file.html 

Finally I created bootable USB using Rufus (also tried ultraiso). easy ah

But when I boot from the USB  it is giving me "windows failed to start"error as if there is no windows file on the USB.

Can anyone please help me.

Thank you very much

Serki