"Secure boot not enabled!" when I boot Ubuntu live CD on Asus Q400A

The message "secure boot not enabled" means that the Secure Boot feature is not enabled on the computer. Secure Boot is a feature that's designed to prevent certain types of malware from running before an OS has booted.

The key point is that the message you see is not an error message, nor is it diagnostic of anything going wrong. Your problem is occuring after that purely informational message has appeared on your screen. Chances are GRUB is flaking out on your computer, since the program that generates the message (shim) launches GRUB immediately afterwards. Given that you've installed Windows 7 on the computer, though, it's not entirely clear that you should even be installing Ubuntu in EFI mode (which is how you're booting it now, given the Secure Boot message). Thus, I recommend you begin by booting a Linux emergency disc (something like Parted Magic), running Boot Info Script, and posting a link to the RESULTS.txt file that it generates. That will tell us about your current configuration, which will help us offer a solution that doesn't involve assumptions and guesswork.

Edit/New Information: Your Boot Info Script output indicates that your Windows installation is clearly in BIOS/CSM/legacy mode. Thus, you should not attempt to install Linux in EFI mode. I'm not sure why the installer is hanging when you try to boot it in that mode, but with any luck the problem will clear up when you attempt a BIOS-mode boot.

You may be able to do this by using your firmware's boot manager, which you typically access by hitting a function key as you power the computer on. (Which function key, unfortunately, is completely non-standardized. Check your documentation or look for an on-screen prompt, which will probably stay visible for only a second or two.) If you can find this menu, with any luck you'll see two entries for your optical drive, one of which will include the string "EFI" or "UEFI" and the other of which will not. Select the non-EFI entry to boot the Ubuntu installer in BIOS/CSM/legacy mode.

If you can't find a boot manager menu or if you can't get it to boot the disc in BIOS/CSM/legacy mode, try downloading the Mac version of the Ubuntu installer. Ironically, that version lacks EFI support, and so may work better for your needs.

I have an Asus q400a. Hold down F2 and you can get into the BIOS settings. There are settings for Secure Boot, for CSM, UEFI etc. there