2 RAM slots not responding

Hardware Motherboards
1

Hey, i'm new to the forums and this community was reccomended to me by a friend. I'm having trouble with a computer i'm building wth my Dad. We have all the components working just fine, with the only problem being that we cannot use all four of our 8GB sticks of RAM, only two. We don't know why the computer won't boot with all four in the slots. All sticks of RAM work, but only in slots A1 and B1.

Specs:

CPU: Intel i7 3770

Mobo: Asus P8 Z77-V Pro Thunderbolt

GPU: AMD Radeon 7870 (Made by Sapphire)

PSU: Corsair HX 750

HD: WD Black Desktop 1TB

SSD: ADATA XPG SX900 256GB

RAM: Corsair Vengeance 1600MHz (4x8GB)

OS: Windows 8 Pro :(

If you have any ideas of what the problem may be, or any solutions, i'd love to hear! Thanks for any support. 

2

It sounds like an error with the motherboard; two dead DIMM slots, probably. I had a dead slot on My Maximus V Formula, and after a rather messy RMA with Asus, I got a new board back that worked. It won't take too long; I'd RMA it.

3

and if you put only 2 sticks in slot A2 and B2 ? if the computer doesn´t boot then RMA the board.