Question 4gb memory not working on 2nd slot

[de6ir]

I have a Gigabyte mb. GA-B75M-HD3. It has 2 memory slots. I have 3 ram modules. 2x4gb (both same specs)and 1x2gb. The problem is pc doesn't boot when a 4gb ram is installed in slot 2. Like this:

Slot 1: 4gb Module A - Slot 2: Empty - Works.
Slot 1: 4gb Module B - Slot 2: Empty - Works.
Slot 1: 2gb Module C - Slot 2: Empty - Works.
Slot 1: 4gg Module A - Slot 2: 2gb Module C- Works.
Slot 1: 4gb Module B - Slot 2: 2gb Module C- Works.
Slot 1: Empty - Slot 2: 2gb Module C- Works.
Slot 1: Empty - Slot 2: 4gb Module A- Doesn't Work.
Slot 1: Empty - Slot 2: 4gb Module B- Doesn't Work.
Slot 1: 4gb Module A - Slot 2: 4gb Module B- Doesn't Work.
Slot 1: 4gb Module B - Slot 2: 4gb Module A- Doesn't Work.
Slot 1: 2gb Module C - Slot 2: 4gb Module A- Doesn't Work.
Slot 1: 2gb Module C - Slot 2: 4gb Module B- Doesn't Work.

Why is this happening and any way to make the 2nd slot work with 4gb modules?

 

[Calvin7]

Memory is guaranteed in the form sold.

Combinations such as you have made have no guarantee to be compatible together.

You are free to do your own compatibility testing with no guarantees.

 

[de6ir]

Memory is guaranteed in the form sold.

Combinations such as you have made have no guarantee to be compatible together.

You are free to do your own compatibility testing with no guarantees.

Sorry but it is not about compatibility testing. It is about a conflict with one of the slots. Maybe an electronical defect or a bios version issue. I don't know. Maybe someone may have a helpful guess.