Bootcamp HELP installing windows7

Hi. I've created a windows 7 disk on my usb.

I've done bootcamp but after bootcamp assistant finishes and when

the computer restarts it says "No bootable device -- insert boot disk and press any key" on a black screen.

Now im wondering I should have my usb format on "MS-DOS (FAT)" or Mac OS Extended (Journaled)

I've also read some articles saying that i should hold down the option key after the chime, but after i did it it just shows up my hard drive and recovery disk.

Im using OS X 10.8.

any help?