I just bought a new ASRock VisionX 420D (Haswell) and did a clean installation of Windows 8.1. After installing all the drivers, it recognizes the card reader in Device Manager, but inserting a known-good SD card doesn't register. If I plug in an external Belkin USB card reader and insert the same SD card, it pops up in Explorer as expected. I have uninstalled and reinstalled the latest Realtek card reader drivers (6.3.xxx) to no avail. It simply doesn't recognize a card being inserted. I have reset the BIOS to defaults, unplugged, rebooted, etc., but nothing seems to work.

Any ideas why this might be happening?