I get this after pressing [enter],

>Loading vmlinuz........
>Boot failed: please change disks and press a key to continue.

I've already tried everything possible and still cannot get into knoppix.
For infomation on my PC.

Acer Aspire Pentium 4 1.7 ghz
768 MB RAM
Aopen External CD Burner
Nero 5 (OEM)

I've already checked the .iso md5 and it turn out Ok using md5summer.
Need some advice and help.