Have you run any stability testing to verify the RAM isn't dying?
Run a memtest either from a boot CD/USB drive or in Windows covering all your RAM
(not sure if this is still applicable with today's MB) Make sure the BIOS backup battery is functioning
Reset the BIOS to factory defaults then change anything necessary to get back into Windows
Test stability in Windows with a stress test application
And of course visually inspect the MB for anything unusual - physical damage, darkened spots, bulging capacitors