Here are a few ideas to try.
When your player is disconnected from your PC and the SD card is removed, does your player behave normally?
(Can you play audio files saved in the internal memory and when you connect to your PC you can see the internal drive folders and files?)
If YES, then maybe your problems are related to the micro SD card.
If NO, then maybe your player needs additional problem solving.
If your micro SD card is causing the problems you described, then maybe trying using the micro SD adapter that came with your memory card and connect directly to your PC. Does Win File Explorer show the standard SanDisk player folders and your audio files? If not, maybe you can think about using the the Windows Error Check Tool (under Properties -> Tools).
If the file allocation table of your memory card is messed up, you may need to consider trying to reformat (FAT32).
Maybe report back here with your results.
