Run Lion from bootable external hard drive

[rjstewart22]

Hi,
First,
let me say I am not very acquainted with the rules of forums or this one in particular so excuse me if I have violated any rules or precedents with this post. A polite redacting reply will get this thread where it needs to be mr. moderator.
Second,
My question. I have a bootable copy of Lion on my 500gb partition WD HD. I am trying to figure out why I can't get my thinkpad ( model unknown I can find it if its necessary) to boot from it. I set as the first priority drive in Bios then backed it down to fourth (the priority before my HDD). I am a tech intermediate at best so layman terms would be greatly appreciated. It is a school laptop so that may have something to do with it.

Thanks all,
Jake Stewart