I used Startup Disk Creator to make a bootable USB stick for Xubuntu 12.04 (and then also for Ubuntu 12.04...).
On restarting the laptop with the stick inserted, I press F9 to select the boot device. The laptop detects the stick and displays the boot option ”USB hard disk”. I choose it. Then I get the message ”boot error”! Same for Ubuntu.
The stick is fine, I can save on it, read it, erase, format...
(Unfortunately, I cannot install any other application, since my OS, Ubuntu 12.04, was somehow corrupted on upgrade from 10.04. It still works but doesn't perform new application setups. And the DVD writer is kaputt after the first 3 years...)