Apple - My SD card slot doesn't work

I blew hard in the SD card hub. Now it is working fine.

This thread says that there's a switch in the SD card slot that detects when a card is inserted, and it can get clogged by dust or jammed or something. If you play around with a toothpick (or anything that fits in that hole), it'll fix your problem. Toggling that switch helps.

for me sticking the SD card in and pulling it a bit out again ( just a few mm ) seems to get it mounted. There's even a video that explains how to put it in and pull it out a bit here

But I find that putting it in under an angle works better: Sticking the card in under a angle with the cut off corner against the top of the SD slot and then pushing the card in seems to get it mounted every time.