Is it possible to disable DDR Dual Channel?

Hi ,
I have an AMD Athlon 64 3000+ motherboard (model name: GA-K8NSC-939).

Until now I had 1 gigabyte of RAM in two ram modules (2x512).
But now I tried to add another RAM module of 1 gigabyte(1x1024), and the computer won’t start.
I tried all the slots combinations possible, as well as tried my new RAM with one of my old ones and it worked (so I had 1.5 gigs of RAM).
This lead me to think it might be something to do with the DDR Dual Channel, but I couldn’t find any way of disabling it.

So my question is : Could this be the reason why my motherboard won’t accept 3 RAM sticks ?
And if so, do you know how to disable the DDR Dual Channel?
Thanks in advance…


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