O.K, so if I am to understand this, you are trying to install an operating system into a laptop with a usb powered optical drive or usb flash drive? Second, post details like what kind of laptop, what operating system? It sounds like you are trying to install an os over an existing os (being new) or to a blank hard drive?
This should be fairly easy once we get some details my friend. If this is a windows 8 or 8.1 deal, chances are you are going to have to disable secure boot in bios, again very easy.