Unable to see my bootable usb/external HDD from boot menu

Hey guys wondering if you could help me...

I'm trying to put windows back on my system (windows7 home pre) and I have created a bootable drive via boot camp then within boot camp I hit the install windows 7 or later version... I already have the latest support software downloaded on another usb.

So this all goes fine but when the computer reboots I get a black screen saying no bootable disk, insert a bootable device and press any key. I do this and get nothing.

So I restart and hold down the alt/option key whilst its booting and my bootable usb doesn't show up. I only get my mac and a recovery disk.

Any ideas?

Thanks in advance

 

Hey... is imac mid 10 27" and yes it did come with a optical drive and still has it in there.

I've tested out and played some random CD's etc and they worked fine... however when I run the bootcamp process and it tells me to insert disc it spits it back out. I have tried the official disk and also a burned iso image but they just get spat out after 30 secs or so.


Also I have managed to install windows 8 on this system via usb or a external hdd and also think I installed windows 7 as well (too far back and cant remember how I did it).