How did you create flash drive? Some have issues with one creator or another, or some brands of flash drives. If you got that far flash drive should work.
There were bugs in old versions of syslinux based installer.
Sometimes these fixes help. Or Sometimes download is not valid and you need to do that again. You can check download with md5sum to verify that it is correct.
syslinux errors help/enter works:
Delete ui in syslinux.cfg
in the directory from "isolinux.cfg" to "syslinux.cfg"
How to create a bootable Ubuntu USB Flash Drive - unetbootin
Usb installer from Windows
If that does not work
Also instructions for DVD or USB