I can`t install Ubuntu.

[charliesll]

I have 3 computers, one with Win7, one with Win8 and one with Win8.1. I tried installing with a CD on all 3, when that
didn`t work i tried a new CD, when that didn`t work I tried a thumb drive. I get the same error message on all of the
computers with both CD`s and the thumb drive. When I reboot it says : operating system couldn`t be loaded because
a required file is missing or contains errors....Any suggestions?

[fantab]

Where did you get Ubuntu CD from? Newer versions of Ubuntu do NOT fit on a CD, is it a DVD?
Download Ubuntu from Here (http://www.ubuntu.com/download/desktop), preferably using Bittorrent Here (http://www.ubuntu.com/download/alternative-downloads).
Then run a MD5Sum check (https://help.ubuntu.com/community/HowToMD5SUM) on the downloaded ubuntu.iso. (If you have the .iso already then run on it as well, if sums don't match re-download).
Then BURN (http://www.ubuntu.com/download/desktop/burn-a-dvd-on-windows) the DVD.

When booting a DVD you must choose the DVD as your first boot device in BIOS/UEFI.

Did Windows came pre-installed your machines?
Dual-Booting with Windows8, especially if its booting in UEFI requires some additional steps on your part... Read more from link below:
https://help.ubuntu.com/community/UEFI
http://ubuntuforums.org/showthread.php?t=2147295&p=12657352#post12657352

Good Luck...