Black screen while playing online game - help

Use some compressed air in a can to blow out all vents, bottom, sides etc. Use the laptop on a hard surface, not on your lap, bed or cushions.
You may need to use a cooling pad to set it on too.

OK, now try the same DIM in another slot, you can stop if any errors show up. We want zero errors in at least 7 passes.

I'll get slapped for this. If your area has no canned air use a vacuum cleaner with a brush to sweep out the bents and grilles. Have the machine off with the battery removed.

Britton30, consider yourself slapped
You can also try an old toothbrush or pencil sized paint brush to remove dust.

Check this youtube video, it may be similar to your laptop, if not then search for one that is: How to clean the cooling vents on a laptop (Asus A8JS)
Make sure the CPU cooling fan is clean, all components you can see, vent screens and vent path.

I would try to fix the overheating issue before you do any more testing. If the CPU or graphics card overheat while running memtest86+ it will throw an error.
If you're getting +90°C at bootup, then it will overheat when doing any kind of testing.

Run memtest86+ with the other RAM card installed, 7 full passes, if you get any errors you can stop the test.

No, you have errors in both slots with one card, test with only the other single card.

If this was my laptop I would fix the overheating issue first, it may be causing the RAM problem.
Your choice.

You should still test one RAM DIMM at time in each slot. A bad board can cause errors too.