RAM issue on Dell T3400

So I have a dell T3400 that I'm upgrading and am using a 7950 in. I have 16gb of DDr2 ECC I believe buffered. The issue is that if I use a single stick of it in my system it causes nothing to show and six beeps(meaning ram issue)
But, if I put in a stick of ram, go into the bios and put in some of the ECC RAM, it shows it in the bois.
So the computer knows what's being put in it, but it isn't allowing me to boot with it. I'm using the latest bios, stock motherboard, E8400 (dual core, 3ghz) radeon 7950, random PSU, 500gb HDD and the rest is stalk.
Any help? I've tried just about everything to get it to work. I know that you can get 4gb dimms on this computer because a lot of other people have been able to. Along with I know that ECC ram works in the PC because it came with 2gb of ECC. But I'm not too sure about the buffered/unbuffered/