shahrazad , OK, so the problem is that your player cannot work properly by itself, but can be detected as a removable drive and show the files via explorer?
If you have not re-flashed your player with another firmware before, then i'll suggest a firmware extraction, repair, and re-flash first.
Extraction & repair guide here http://www.mympxplayer.org/how-to-extract-firmware-of-your-player-using-the-s1fwx-tool-vt66.html
Re-flash guide here http://www.mympxplayer.org/how-to-update-the-firmware-for-your-mp3-mp4-player-vt46.html
If it does not work, then i'll suggest that you try all the v3.5.xx series firmwares in the downloads section for your screen size, until you get a working one.