First off, I did read through most of the replies to problems similar to mine but none of the solutions worked for me.
Here's what I did: I plugged the memory card into my laptop with the adapter and it worked fine, but when I tried to transfer some music on it, it didn't let me. I unplugged it and plugged it in again. It prompted me to format it, but when I tried to, it said it cannot be formatted because it's "read-only" or something. And now the it won't show up on my laptop *or* in my phone. It doesn't show up in Device Manager or Disk Management and there's no lock switch on the adapter either.