Generaly doesn't happen, my guess would be a bad burn.
Try md5ing the iso and see if its correct (you can get the .md5 file at the mirrors.)
www.md5summer.com
I'm not quite sure as to the cause of this, but I will do my best to lay out all variables here to see if anyone can offer some advice.
I have been downloading various LiveCD's from several distrobutions of *nix, to incl. FreeBSD, Morphix, Gentoo, Knoppix, etc. all in an effort to see which distro I might prefer to run. I encountered a couple boot problems with a couple of the Distros, but by far Gentoo and Morphix have been the best and most stable. When I burned off a copy of the Knoppix LiveCD last night, and attempted to boot, I thought I had a minimal problem.
The boot process began from the CD as normal (read the bootstrap on the CD and asked for "boot:") Following my enter of "knoppix" it (as usual) changed the screen to the black screen with the Linux penguin in the top left corner. No text displayed to show boot status, and the cursor never moved from beneath the pengiun. I let it sit for a couple minutes, figuring maybe it was just slow, or was having a difficult time probing something. Much to my dismay, it still did nothing. So I rebooted, to re-attempted the process. Upon rebooting, as my BIOS was detecting HDD's, my display started to show large colored blocks. Something you might see if your video cable wasn't plugged in good. as the BIOS was finishing it's POST, it got worse and turned into vertical lines of multiple colors that would flicker and strobe as the BIOS's output flowed. After POST, it just stayed that way.
Rebooting gave the same results, only worse...it then displayed nothing but the lines. No blocks like before. So at this point I'm flipping out paraying my GeForce FX 5700 wasn't fried. I tried different cables to the monitor. I tried different monitors. I tried swapping the card with another machine using an 8X AGP card (FX 5600). I tried swapping with an AGP 4X card, thinking something on the mobo was screwy. My card (5700) worked fine in two other machines, but when placed back in mine, it would screw up again. The other two vid cards worked fine in my machine, no lines.
After a few (3) hours of this, and exhausting everything I could think of, I resorted to resetting the CMOS jumper. Once again, using my card, I tried to boot. BIOS!!! I SEE BIOS!!!. Ok, I go into the CMOS, put my normal settings in there which have been used for a good 6 months, so I know MY settings are ok. Here's what I found though, somehow, the voltage had to have been changed for the AGP output. After clearing the CMOS, was the only time I could get a picture, and the only way to maintain it was to bump AGP voltage up to 1.6v from 1.5v. This has since stopped the lines all together, and my display is back to normal.
What I wanna know, is how the hell my output voltage got changed while Knoppix was trying to probe my machine.
Generaly doesn't happen, my guess would be a bad burn.
Try md5ing the iso and see if its correct (you can get the .md5 file at the mirrors.)
www.md5summer.com

A8PicoCart Multicart for Atari 800xl /65xe / 130xe / XEGS
$16.95
Atari 130 XE/Atari 1050 Bundle W/ Cords And Extras (Powered On)
$300.00
GreaseWeazle v4 board USB floppy drive adapter Retro All Formats
$35.00
DEFECTIVE Atari 810 Vintage Computer Disk Drive powers on Unit Only Boo G3D
$49.29
Atari 1040ST Vintage Home Computer | Turns On
$299.99
Fujinet 1.7.1 Atari 400 800 800XL 130XE 65XE XEGS Assembled, Tested, Working
$99.99
ATARI Mouse with Adapter for ST, STE, Mega STE, TT Optical - USA Seller
$29.99
GORF Atari/Roklan 400/800 Cartridge Brand New In Box
$48.00
VTG Atari 130XE Home Computer System 130 XE Parts or Repair READ
$150.00
READ UNTESTED But Works Vintage Atari 410 Program Recorder
$34.50