Q: I have done the steps. Finding the external disk during boot. But the installer does not start. What has gone wrong?

I created the install drive on a external USB drive. Everything worked and I got the External drive with the installation package on it.

When I choose to boot from it I get a crossed over circle (error I presume) and after a few seconds the computer just shut down.

Done the procedure twice, once to a flash drive and second to a external 3.5 SATA drive connected via  USB.