[SOLVED] Problem trying to boot from USB flash drive

I've had this problem several times with Ubuntu distro and other distros.
In the latest case I've downloaded the Zorin distro and used Startup Disk Creator to attempt to create a bootable USB flash drive that way.
On booting I see Syslinux info, then boot: followed by a flashing cursor and distro does not then proceed to boot.
Help please.