I have the same mp3 player, and it did exactly the same thing. When I first connected it, the computer saw it and installed the software. I put some music on it and it played fine. When I plugged it into my computer again, the computer wouldn't recognize it and tries looking for
drivers for "unknown MTP device". I've tried plugging it into several other computers and nothing will recognize it. I tried taking the batteries out to reset it, but that didn't work either. Everything I read online expects it to be recognized as soon as you plug it in, which it doesn't. I know i can't be the only one having this problem.