I followed the steps in http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-windows and know that my USB stick is bootable.
It starts booting, but then shows an error message:
cannot find an operating system.
I have used the same setup and installed it by double clicking the wubi.exe from Windows -- it downloaded ubuntu-12.04.3-wubi-amd64.tar.xz and installed.
So I know it is the right OS, but I am having trouble installing from my bootable USB stick. What should I do?