Sorry Geekgal that it's taken me so long to get back to you on this.
I have a few thoughts, some of which I do not care to post on this sight...
In the meantime...
Visually examine the surface of the CD's you are trying to start up from. If it's badly scratched or marred, it's possible the drive is too finicky to read it.
The B/W refers to "Blue and White". Sounds like the machine you are referring to. A blue tower with a hinged side panel for accessing the guts? Make sure the drive cables are properlly seated. Open the panel towrd you and the drive should sit in the right hand corner. This should be easy to do. Two cables...
You also want to reset the PRAM. Apple tech article located at
.
Basically start the machine (from power "off"

holding down OPTION-APPLE-P-R keys. Five startup chimes, then release.
You can also reset the CUDA chip on the motherboard though I would try this mostly in a "will not power on" scenario rather than a flashing question mark scenario.
We can discuss this further if need be. You'll see the CUDA reset button(s) on the motherborad between the heat sink and hte clock battery.
Hope this helps...
MacGeneral