[clug] Why does my motherboard hate me?

[Michael Still]

Hi.

I have a Gigabyte AM3 motherboard (specifically a GA-MA785GM-US2H) which 
takes DDR2 800Mhz memory. I have a dual core AM2 CPU in the machine if 
that matters.

The machine worked fine with 2 * 1GB DDR2 memory. I just tried to 
upgrade to 4 * 2GB DDR2 memory, which the motherboard manual says should 
be supported. However, in this configuration the machine doesn't boot. 
It doesn't even get to the BIOS, it just reads from the empty DVD drive 
over and over. The machine does boot with just 2 * 2GB though.

Any hints?

Thanks,
Mikal