Trying to Install Windows 7 onto MBP Mid-2010 but I get this "No bootable device -- Insert boot disk and press any key". What do I do?

I'm trying to install Windows 7 onto my MacBook Pro Mid-2010 (MacBookPro6,2) from a USB drive, since my Super Drive no longer will burn DVDs or CDs. I did the XCODE trick to allow me to make the bootable USB. But when it reboots after partitioning I get this, "No bootable device -- Insert boot disk and press any key" message. When I press a key after reinserting the USB it still won't boot after pressing a key. I unplugged anything connected to it and it still doesn't work. Is there any way I can get it to be recongized or do I just need to get an external disc drive and burn a disc that way?