Run Windows Memtest. It'll stress your memory much better than Prime and find errors easier:
Run one instance of it for each stick that you have, and pay attention to how much it tells you to test once you click on "start testing." Type whatever amount it gives you into each window.
And keep an eye on your memory temps, because the sticks will get hot. If you don't have heatspreaders and they feel they're getting too hot, then just run the "blend" test in Prime.