Need hel badly RAM issue

[MarcusLibelus]

I have here an fairly old system

 

msi z77a-g43 

i5 2500k

4x4gb corsair 1600hz ram

 

the problem is that my bios and windows can only read 8gb or ram BUT the bios and cpuz can detect the total amount of ram(16gb for this case)

tried eveything that i know, tested each ram in each slot one by one, did bios update, switch bios, did cmos clear, did reseat the procie, the voltage also is right 1.5v

it can read 8gb if i plug in 2 stick( i already tried all combination)if i start to plug in the 3rd one, it will not show 12gb but only 8gb BUT the bios can detect it

 

need help badly, did i miss something to do? do i need to replace something, thanks in advance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Cyracus]

are they matching ram sticks, you said corsair but like vengeance 1600mhz same timings and everything because mixing ram can make systems act stupid sometimes. beyond that idk