I have an iMac configured as follows - Screen 27" CPU 3.4 GHz i7 Graphics AMD Radeon HD 6970 1024 MB I downloaded Ubuntu version 11.10 64 bit ISO and burnt that to both DVD and USB stick as per the instructions on Ubuntu's download page. Neither will boot. Symptoms are as follows - DVD: When the iMac is restarted and booted from DVD (labelled…