How to unlock memory on a Gigabyte GA-Z77X-UD3H (UEFI BIOS)

[Roguery]

On the system specs of the UEFI BIOS it says I have ~32gb of memory, but in spite of this I can't access more than 16gb. I've gone under advanced memory settings and it only appears to be legitimately registering two of them (i.e. it only gives me options to do things with two of them). I'm trying to get them to work but I'm not having any luck. Any help would be great!
Oh by the by, they're G.Skill Ripjaws X Series 240-pin DDR3 1600

Edit: Ran a full memtest on all of them. It registered that there were four and they all passed the tests without a single error.

 

[cars12345]

What version of Windows do you have? 64-bit?
Does Windows say that you only have 16GB?

 

[Roguery]

What version of Windows do you have? 64-bit?
Does Windows say that you only have 16GB?

Windows 7 64-bit
Windows says that I have 32gb installed physical memory, 16gb total physical memory, and 13.7gb available physical memory

 

[cars12345]

Do you have Windows 7 Home Premium 64-bit? This version only supports 16GB max of RAM.
http/msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#physical_memory_limits_windows_7

 

[Roguery]

Do you have Windows 7 Home Premium 64-bit? This version only supports 16GB max of RAM.
http/msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#physical_memory_limits_windows_7

I think you may have hit the nail on the head there. Thanks!
Off to upgrade OS I go.