weird ram problem

So I bought a new motherboard, an Asrock DualVsta775 and installed my 2x512 ddr400 ram on it. My problem is, only one of the 512 ram worked. I tried changing slots, using one ram at a time, playing with the settings on the bios, I still can't get both 512 rams to work. And they work on another computer. The other problem is, after playing with the settings on the bios, somehow both rams aren't detected anymore. I just get 3 beeps on post. I tried clearing the cmos following the manual's instructions but it didn't seem to work. So what do I do? I am considering buying some ddr2 ram but first I would like to try to fix that problem.

Oh and the only thing I did in the bios was change the ram frequency to 200mhz (ddr400) since it was at 166mhz (ddr333).

Those wacky ASRock boards can be flacky. Make sure your RAM is a brand prettymuch guaruanteed to work, like Corsair or OCz. Try the RAM in a different motherboard.

Yeah the ram works in another mobo. They weird things is that both rams are the same brand (kingston) but only one of them works.