Hardware reserved memory is used by the motherboard, GPU etc.
It can also depend on how big your page file is. Press Windows + X and go to System. Then go to Advanced System Settings and then Settings under Performance. Click the Advanced tab and where it says virtual memory - How much does it say it's using?
In the BIOS there will be an option to specify how much memory the graphics can use. Id start by looking in there.
I've also read that It could be a motherboard issue (issue with your sticks or slots).
Maybe you should take out all the memory and added them one by one and check the combination.
I can see your motherboard as 4 slots. They're in pairs of blue and white.
How many memory modules are you using? 4 x 4GB?
Are they all the same model?
You need to pair them, white white and blue blue.