For the benefit of anybody who is having problems installing Linux on the Acer E11 netbook:
http://www.zdnet.com/article/install...er-aspire-e11/
Changing Acer F12 Boot Menu option to Enable:
https://www.youtube.com/watch?v=KycrBtjuJHc
You should be able to use the UEFI boot (instead of using Legacy) with your USB HDD, without disabling Secure Boot.
If you prefer to disable SB and use Legacy then:
Changing BIOS mode from UEFI...