[H] Old Intel P4 questions

[Thane Sherrington]

I have an older PC (well not older in Duncan's sense, but older) :) - 
it has an SL79L processor 
(http://processorfinder.intel.com/details.aspx?sSpec=SL79L) and it 
won't boot (00 on the POST card.)  The CPU won't work in another 
machine that works with an SL69Z 
(http://processorfinder.intel.com/details.aspx?sSpec=SL6ZY) and the 
SL69Z won't work in the original machine.

So my problem is: do I have a dead motherboard and CPU or a dead 
motherboard or CPU and imcompatible CPUs?

Is there something that would make a machine that can handle an SL79L 
unable to use an SL69Z or vice versa?  It's the same package, the 
same core voltages, but the bus and multipliers are 
different.  Surely the SL79L should work in a slower motherboard.

T