New to the forum (and to OS coding really) except for writing a pmode system for DOS so many years ago I can hardly remember

I've started working on an OS purely for interest sake and have gone with a 2 stage boot-loader design.
Sofar all the bits of it have come together under bochs nicely (using floppy image).
I just wanted to find out if A) there are any "code" differences one should take into account when booting from a USB device, or CD for that matter.
I thought I'd take the time now to test what I have sofar on a few real machines and setups, starting with a USB boot on my laptop.
I've written the 1st and 2nd stage loaders to a USB memory stick but I'm not having any joy in getting it to boot.. All i get is either a flashing cursor (not even executing/loading the 1st stage) or a message that the media is not bootable.
I'm running an AMI bios in this laptop, are there any known problems with it booting of USB?
Lots of questions..
