2.6 kernel won't reboot on AMD system (no, not the BIOS...)

["David N. Welton" <davidw@eidetix.com>]

[ Please CC replies to me. ]

[ Sorry for the rerun, but I guess everyone was away at the OLS, so I'll 
try again, operating on the squeaky wheel principle. ]

Before you hit reply or erase, no, I'm not talking about the machine not
getting past the BIOS check complaining that there is no keyboard present.

Kernel 2.6.7

model name      : AMD Athlon(tm) XP 2400+

motherboard: http://www.ecsusa.com/products/km400-m2.html

... not sure what else might be useful... apci=off added to boot
options.  Preemptive kernel.

In any case, the machine in question does not reboot.  I traced the
problem down to the mach_reboot but it doesn't get past those assembly
instructions.  Things do seem to work alright if a keyboard is
installed.  Otherwise, the machine just sits there, no longer responsive
to pings or anything else.

This appears to be a somewhat common problem, as I found several other
posters discussing it:

http://lkml.org/lkml/2004/3/12/248

http://marc.theaimsgroup.com/?l=linux-kernel&m=108868695814658&w=2

any ideas on what parts of the kernel to look at in order to determine
what is causing this?  I need to fix it, and I don't know where to start 
looking.

Thankyou,
-- 
David N. Welton
davidw@eidetix.com