Identifying faulty RAM, and installing good sticks

[HelpframePrime]

Trying to find whether the problem is my motherboard or the RAM sticks.

I built a PC last year (Asus Maximus VIII Ranger Z170, Intel i7 6700K, Gigabyte GTX980 6GB, H80i Water Cooler) and had 4x4gb of RAM purchased for me as a gift. However, when I tried to install them together, the PC refused to boot. IIRC the number displayed was 99 a lot of the time. I tried to put them into pairs, but again, same thing.

I've been running it with just one stick of 4GB RAM, but with recent updates and recent games it's seriously struggling. I plan on trying all 4 sticks in again when I get home tonight, but while I'm stuck at work, are there any tips and tricks I could use to ensure the smoothest process possible to either getting them all working in the PC, or diagnosing which stick is faulty so I can send them back and buy another pair (probably a set of 2x8GBs)?

 

[helpstar]

update the BIOS to the latest version
clear cmos

check the motherboard´s CPU socket for bent pins

 

[drkatz42]

You can use windows diagnostic utility for each stick of ram.
http://www.pcworld.com/article/3040544/hardware/do-you-have-bad-ram-heres-how-to-find-out.html

When you're in the utility, you can have it run the extended tests which I advise.

 

[DRagor]

So your PC works with one stick, right? Then first thing to do is: use all 4 sticks you have, one at a time, in the slot you're currently using, to find out if each of sticks is good. If even one will not post, send back whole set.
If all 4 work individually, you need to find out if all 4 slots on motherboard work correctly. So use 1 stick and test each slot one by one. If even on of the slots will not post, first check CPU socket for bent pins, as it is sometimes the cause for such problem. (Note the motherboard manual often will tell which slot(s) should be populated first. But when using just 1 stick, healthy motherboard should post with any slot used).
However, if both those tests are passed, it gets tricky, as you wrote that pairs don't work.