Hi!
Almost all laptops can boot without the internal hard drive, but only to the BIOS - there is nothing else you will be able to do.
You cannot boot from an external drive per se, you can have a Windows Installation Medium installed on that drive (but this will only work if there is an internal hard drive - the point of the installation media is to get Windows insalled on that PC) or you can create a Linux Live USB key from which you will be able to boot.