I've booted Knoppix v3.8.2-2005.05.05EN on my laptop (A Dell Inspiron 8100) without problem. When I tried it on my desktop I got:

hdd: cdrom_pc_intr: The drive appears confused (ireason=0x01)
irq 18: nobody cared!
handlers:
[<c02356d8] (ide_intr+0x0/0x120)
[<c02356d8] (ide_intr+0x0/0x120)
Disabling IRQ #18
Welcome to the Knoppix live-linux on CD
Scanning for USB/firewire devices...... done
Can't find Knoppix filesystem, sorry.
Dropping you to a (very limited) shell.
Press reset button to quit.
Additional built-in commands available:
cat mount umount
insmod rmmod lsmod


etc, etc, etc.
The motherboard is an ASUS P4P800 Deluxe, with a P4/2.6 GHz processor and 1024 Mb of RAM.

Any help with diagnosing would be appreciated


Cheers

Greg