Right, that's the newest one (I have revision D cart as well).
What type of micro sd cards do you have? What size (2GB, 4GB etc), what brand (Kingston, Sandisk etc)? If I remember correctly, the largest sd card this flashcart supports normally is 32GB. What file system have you formatted the cards with (exFat, FAT32 etc)? I think for this cart recommended format should be FAT32 (for 2GB card it should be FAT16). Can you try to properly format your sd card with this program (
SD Formatter 4.0) just to see if it makes a difference (assuming you haven't done this already)? And lastly, the black screen, is it just blank screen, or does it say something like "an error has occurred"?
It might be that your cart is just defective unfortunately. If it turns out that the cart is defective, I would contact 3ds-cart.com and ask them about it. I'm not familiar with 3ds-cart.com, but I would imagine they will replace it, give your money back, try to help you with it or something.