cannot boot into my bootable usb which contains windows 7 HELP! - SOLVED

hello

i have dell studio xps 435mt, with one ssd (contains windows vista) and one normal drive.

i have created a bootable usb drive with poweriso.

when i find the scandisc usb in bootlist and enter it, i get a text that says something like: no diagnostic utility partition identified

what is happening?

edit: just change first hdd priority in bios to the usb that is connected