I downloaded a Knoppix 6.7 DVD, verified MD5, burned a DVD, verified a good DVD and good boot on an Intel desktop. But I am trying to boot this DVD on my iMac. The boot begins normally, I see the boot prompt and can respond to it, and I can see the boot messages fly by right up until "starting hardware abstraction layer". Then the screen goes completely black. The DVD continues to whir and the sultry voice says we are starting, so sound card works. The keyboard and mouse are completely unresponsive beyond this point. I've tried debug, expert, knoppix 2, and various combinations of noacpi, noapm, failsafe, screen=2560x1440, no3d, desktop=kde, xmodule=ati, xmodule=radeon, xmodule=fbdev, norandr, nofb nodrm vga=normal. CTL-ALT-F2 does nothing --- ever. The same blank screen happens in text mode. The only way out at this point is to power cycle the machine. One of the above combinations (failsafe) caused a shell prompt to appear for less than a second before the screen blanked. When the screen goes black, it usually does so in two stages. First all the boot messages disappear and the screen has an all black background, but appears "lighted". The it goes completely dark, as if the power were just shut off. There are no flashes of words or lines or graphics -- just goes black. The boot messages indicate my graphics card has been detected as "ATI 9488" for an ATI Radeon HD 4670 wtih 256MB VRAM on PCIe bus with device ID 9488. The machine is an Apple iMac Intel 3.06 Mhz core 2 Duo with 4GB of memory and 3MB of L2 Cache. I'm using a usb keyboard and mouse and booting from a USB connected external DVD. (internal DVD scratches media) I've searched this forum for "iMac" with no results and tried Google. Any help would be very greatly appreciated. Thank you much in advance.