This has just happened to me. I think the micro SD card has failed. I've tried cleaning it, but I know it was perfectly clean as I hadn't let it touch anything between going from packet to card slot. It worked a while in 2 different devices. It failed while inside the 2nd device (had been working fine, then simply not found and it wasn't physically touched or removed in between). So I know it's a fail. Also checked in the 2nd device and it's unrecognised there. I'd only taken it out of the package over a week ago. It's a Kingston, and cheap. A sizable number of reviews in Amazon, where I bought it, say the same card sold failed while more say it's good and long lasting. Some manufacturers cards' quality may vary from card to card. On the other hand it could be from a virus through Android web connection.