Dual Channel not working on Mobo

[Pointbox]

I have an existing kit of RAM on my mobo (2x4GB) 8GB. I bought a second kit of the same exact kit of RAM to use in dual channel mode and bring my total of RAM to 16GB. I put the new second kit of RAM into slots 2 & 4. When I started my computer I wouldn't have any output to my monitor and my keyboard and mouse wouldn't work. I took the RAM out of slots 1 & 3 to see if the second kit of RAM wasn't working or if slots 2 & 4 were broke. When I started the computer it worked perfectly. The kits of RAM work perfectly when separate but not together in dual channel mode. I have the voltage set correctly on the RAM too. I don't know what the problem is, please help!
MOBO: MSI Gaming 970
CPU: AMD FX-8320
RAM: Corsair Vengeance Pro Series 8GB (2x4GB) 2400MHz C11 Kit (used in 2133MHz because Mobo max)

 

[Tradesman1]

Yes, happens all the time, there's no guarantees when mixing DRAM, see may article, item 2 here:

http://www.tomshardware.com/reviews/ddr-dram-myths,4155.html#p7

TO try will prob need a decent OC on the CPU then starting with one set raise the DRAM voltage to 1.7 and the CPU/NB voltage to 1.3 may need up to 1.35