As you know Nintendo's v1.4 Update blocked flashcarts. To fix this, the m3i team has released an update for their product's reprogrammable core. Here's how to update it.
Make sure to have you flashcart, the cable, the SD Adapter and a SD Card properly formatted to FAT32. Before continuing, make sure the core data file is on the root of your SD Card. You can download the core here. Make sure to unzip it and place the .dat file on the root of the SD Card.
Once the core file is on your SD Card, Place the SD Card into the cart.
Next plug in the thin side of the cable into the flashcart, the port for the cable should be on the opposite side of the SD Slot on the cart.
Next plug in the USB Side of the cable into your PC that should be powered on. If you did everything correctly, the flashcart should start blinking.
Once the blinking has stopped, you may remove your flashcart. if no light appears, you may have plugged in the Flashcart side of the cable the wrong way or you may not have setup the f_core properly.