If you say the machine crashes when you put in 2 sticks but is stable on a single stick there are a few things to try: -
- Try the other stick on its own to narrow down that the issue is on 1 of the sticks
- The motherboard has 4 slots so if its crashing on 1 of the pairs say 1 & 3 then try slots 2 & 4 to narrow down if its an issue with the motherboard slot or not.
- If you have another pair of RAM sticks try those to confirm that it works well on other RAM
Also take note when you do insert the sticks that they align well and go all the way in. A slight miss-align can cause your symptoms.
These steps should help to identify which is the faulty part. Once you can confirm that there is one of the sticks or motherboard that's faulty go n RMA