Hi.
This might be too simple an anwser but sometimes I forget to do this:
Make sure that the computer is set to boot from the CDROM first, before any other devices. You will have to change this on the BIOS, see your motherboard's manual.
Another solution is to check out my reply to the
Booting Mandrakemove thread, for information on how to check if you have a corrupted ISO image file.
PS. You will still need CD3. Yes, you can just click on "Cancel" when the installation requires it, and Mandrake will install and boot "just fine" but there are alot of good applications in that CD that make it ALOT better!