Problems Installing Windows 7 via external hard drive.

I purchased the ISO for Windows 7 Ultimate, and used PowerISO to mount the ISO onto my CD Drive then I copied the files to my Western Digital 320 GB external hard drive. I did all of the prior requirements that were needed such as making sure the boot code was correct I used the following in command prompt under administrator: bootsect.exe /nt60 /fixmbr. I then proceeded to change the boot order for the external hard drive to boot first and put my current hard drive that is installed booting last in order not to confuse the BIOS. Yet when I restart my computer all that I get is a small blinking underscore, and it will not proceed any further. I know that I could burn the ISO to a DVD-R or put it on a Flash Drive, but I don't have any money currently. Can anyone help me proceed past this point please?