Installing windows vista via usb ?

Hi, I'm in dire need of someone's help please, I'm trying to fix a friends computer from my work, When the computer boots up it just goes into a black screen with a flashing cursor and does nothing....
I've tried the obvious F8, It's boot menu, and bios, But because the computer has a usb keyboard, I cant get to change the options of booting from a HDD, Cd/dvd drive, So it's hopeless trying to boot there vista disk from there computer (sata). My computer offcourse has the opposite, So i cant plug it into mine to load windows that way, I do have a sata usb external case, But i cant boot windows from an external usb drive, Can Anyone please point me in the right direction as to how to re-install windows.
Re-cap:- I cant 'boot from cd' as there computer wont let me into the set up options to change the boot order,

Thanks for any advice ray: