After adding more memory to my system (2 4GB modules), it begins crashing approximately every 12-24 hours with a 0x124 BSOD, which a quick Google search turns up to be a "hardware alarm". After doing some testing, I thought the new modules were bad so I sent in an RMA and got them replaced, but the exact same problem exists with the new modules.
I have 2 2GB modules, and 2 4GB modules (the new ones). There are 2 white slots, and two blue slots on the board. With some configurations it works with some others it doesn't.
2GB modules in white slots: Stable 4GB modules in white slots: Unstable 2GB modules in white slots, 4GB modules in blue slots: Unstable 4GB modules in white slots, 2GB modules in blue slots: No POST (I assume this is a "feature" of the board, the previous slots have to be full with identical or higher capacity RAM for later slots to work) Modules in blue slots, white slots empty: No POST
All the modules are ADATA DDR3 1333 1.5v, the only difference is the amount of available memory. It works fine with the old modules, but any configuration with the new modules in it is unstable.
Motherboard: Gigabyte GA-P55-USB3 (default timing and voltage settings) OS: Windows 7 Professional SP1 x64
Testing the modules with Memtest86+ overnight turns up no errors.
More about0x124 bsod installing
Test the RAM sticks one at a time with memtest86+
I have heard that there is theoretically the possibility that sometimes things are picked up with only 1 stick inserted that are missed with multiple sticks inserted at once.
I ran multiple passes of Memtest with each module one at a time, and no errors turned up. I'm running with just one of the modules now to see if the system remains stable.