Hi - so i have 768 kingston ddr 400. Felt like spending some cash - bought an extra 1024 ddr400 same ram. Stuck it in, it registered 1024 ram, felt gutted.
I know had 3 * 512 chips and 1 * 256. When i have just the 3 512 , it works fine, detects it all, stick the 256 in and it brings it down to some silly number like 1040 megs of ram. I know the 256 ram is in perfect working order - my motherboard model is the Ga-7n400 i think

just of the top of my head.
Any explanation would be fandabydosey