Strange RAM problem

So a while ago my computer was acting up and would randomly freeze while gaming mostly, between 5m - 2hrs during gaming. It was pretty random and would sometimes even go a month without locking up. It seemed like I fixed it by changing my memory allocation in the advanced computer settings.. I think it was 4000 before, now it's 8000. Hasn't froze since then, and that was about two months ago. Just a few weeks ago I bought two more sticks of RAM and popped them on my board... now all of the sudden it's crashing again... I'm wondering if I have to change this number again, or if it could be something else?The RAM are all G.Skill and all the same model. 4x2GB sticks.

FYI, if I remove the two new sticks, my computer won't lock up during gaming.

Specs:
MOBO: m4a87td-evo
Memory: G.Skill ripjaw ddr3 1600
CPU: AMD phenom II x4 955
GPU: nvidia gtx 660 ti
HD: Samsung spinpoint F3
PSU: Antec Earthwatts EA-650w