Two sticks of RAM are driving me nuts

Hi Folks.

I've had a stick of 1gb DDR2 PC2-6400 (800mhz) RAM which is double sided. A few days ago I bought another 1gb stick here (it's Rendition RAM). It's the same speed and size but it's a single sided stick.

Now when I put both sticks in together my computer makes some slight audio ticking noises and it sounds like it powers up but the monitor doesn't respond at all. Now when I take the new stick out and power up again the same problem occurs (with the one original stick). However when I take that original stick out and move it to the other RAM slot it powers up fine.

If I then put the new stick in with the original stick the problem happens again and I have to take the new stick out and move the old stick to the other slot before it powers up again properly. I now have the new stick in by itself and it's working fine, but it doesn't work with my old stick in and vise-versa.

I've tried changing the voltage (put it up by 0.5v) but no luck. I also changed the RAM frequency to 677 or whatever it is (instead of 800mhz standard) no luck. I also wiped the CMOS but that didn't work either. According to the Motherboard specs it should support it. It has two RAM slots (both different coloured but I'm not sure if that means anything).

My motherboard is an MSI K9VGM-V.

Windows XP 64x
AMD athlon 64 4400+ dual core
Colors-IT 600w PSU
Sparkle GeForce 8400GS

I really appreciate anyone's help thank you.