Corsair XMS3 only gives half of what its supposed to.

Hello people!

First of all id like to say i am a complete tool when it comes to computers but please try and understand me.

I have a problem with memory on my computer yeah. I have 2 corsair xms3 2x2 gb ddr3 1333 mhz sticks that i have had for about 2 years now. The past year i have been out of my country and didnt use my pc for all that time. So when i came back some weeks ago my motherboard didnt wanna work anymore so i bought a new motherboard and cpu. Everything works great except the memories. A year ago they showed the correct amount of memory which would be 8 gb. Now they just show half of that (2048 mb each according to cpu-z). Funny enough my dad has the exact same kind of memories, xms 3 2x2 gb that he bought not more than 2 months ago and those memories do the same thing. They only show half of what they are supposed to. I tried his memories in my pc and vice versa but still the same result. Also i did add 2 older memories to the other 2 slots on the motherboard and they show the correct amount so its definitely something with the corsair memories.. right?

I should add that i have windows 7 64 on my machine.

Somebody has any idea what is going on?

Thank you so much in advance!