KN8 Ultra not posting (or not letting on that it has posted)

I submitted this query to ABit Tech Support a week ago but haven't gotten a
response. Can anyone here help?

KN8 Ultra motherboard
AMD 64 x2 3800 processor
1GB Kingston PC3200 RAM (2x512GB)
1GB PNY PC3200 RAM (2x512GB)
PNY GeForce 6600GT videocard
Antec SmartPower2 500W power supply
WD Caviar SE drives (disconected at this point)
Wired USB keyboard & mouse

On power up the fans run but no signal is sent to the monitor or keyboard.
I have tested all of the power supply lines with an ATX power supply tester
and tested the graphics card in another system, where both of its DVI/VGA
ports are fine. The system had been working properly since I built it in
January 2006. I have disconnected all drives and cards except the graphics
card with no change in symptoms. I have performed all of the suggested steps
of clearing the CMOS, including with power supply cables disconnected. I
also tried starting without the graphics card. In that case the system
speaker emitted a continuous beep. No post beeps occurred with the card in
place, except for one beep when I tried running without RAM. (I also tried
eachpair of RAM modules by itself, in both bank positions,) I have tried PS2
and USB keyboards. Neither shows any signs of initializing, nor does Insert
or Delete have any effect. Just about the only thing I don't have a way of
testing independently from the mother board is the processor. Since I can't
boot the system, I can't check to see the motherboard BIOS version, but I
have been keeping it up to date.

What should I do next? Can I avoid having to buy another motherboard or
processor to swap in to see if it makes a difference? If not, any odea
whether it is more likely a motherboard or processor problem?

Thanks,
Henry