I have 2 adapters for my micro SD HC card. The first time I put it in, it didn't work. The adapter was recognized, but the memory card in the adapter did not get recognized. I replugged it, and it worked. I put in songs...and as I was about to put in my 18th or so, it just closed out of nowhere. I replugged it again, and it didn't work again.
Of course, I tried the other adapter, and same problem.
After many frustrating attempts of plugging in the USB cord back in and out, I realized that the adapter didn't fit well into the port because the parts inside weren't lined up well with the plastic covering. I just took apart the plastic that it was in and fit in the adapter. Finally, it worked.
It's quite annoying to pick apart the plastic and put it back in for each use, but hey, it works. It feels cheap; I mean, it's weak plastic. But it's cheap, so you get what you pay for.
Update: The card reader fails to work at all now. I bought a different card reader and it works. So the culprit is the reader.