For about a month, I've been using a computer with a ASUS M4N98TD EVO motherboard along with 2x2GB Corsair DDR3 1333MHz's. This worked fine for a while, but my computer recently shut down and wouldn't start again. The DRAM LED light was lit continously, and after a whole lot of reseating of the memories and pressing the MemOK! button, I got it to work again, for a couple of hours. However, now it's failed again and this time the light doesn't indicate anything wrong with the RAMs, and reseating and pressing the button doesn't work either. It doesn't work to use only one of the memory sticks, either (I've tried both of them separately).
What I'm wondering is whether this indicates a faulty motherboard or faulty RAMs or if there's anything I can do to find out which one doesn't work.
Have you tried your RAM in a known-to-be-working board? Do you have access to another stick of good DDR3 RAM?
Based on your description, and that it is highly unlikely that both of your sticks failed, I think it's the board.