If you've recently bought a Lenovo Think Center, or any other PC that's "Windows 8 Enabled", you've likely discovered that you can't install your own choice of operating system (i.e. Linux) on it, it just keeps coming up "operating system not found".
This is because of a 'feature' called UEFI, which is basically a new form of bootloader that only very recent (as of Feb 2013) operating systems support. In order to boot from CD on recent PC's, you need to find the BIOS settings for this and turn it off.
On the Lenovo Think Center this setting is in 'Startup' and is called 'CSM'. Given that this is a vitally important setting to configure your PC, you'd think that a three-letter-acronym might not be the best choice for naming it. Better to name it something like "Enable Loading Legacy Operating systems" or "Disable Lenovo Useless Brick Mode". But no, it's just 'CSM' for 'Compatiblity Support Module'. You need to enable this in order to load your choice of operating system.
Another setting that might be relevant is under the 'Security' tab. This setting is 'Secure Boot'. You might need to disable this, or set it to 'setup mode' to allow installing of a new operating system.
Well, this is what worked for me. Hopefully this post will help others.