Ubuntu bootable USB not at all detected

Try these:

Change UEFI to legacy boot support in the BIOS setup

install ubuntu in USB drive using a software instead of manually from CMD or terminal.

If your new computer came pre-installed with Windows 8, there are a few BIOS level settings that prevent you from booting off your USB device or any other media (CD/DVD) other then your Windows 8 install, all by default.

1. Secure Boot: [Enabled] (http://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface#Secure_boot)
2. OS Mode Selection: [UEFI OS] (http://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface#Compatibility_Support_Module)

I Disabled Secure Boot and for (2) look for "CSM" or "Legacy" Boot support.