After I plugged my Sony MP3 player (model NWZS639FBLK) into our 2014 Honda Accord EX-L's USB port and selected "iPod" in the car's menu, the player got stuck on the startup screen where it says "Every moment has its music". I tried pushing buttons, resetting the player using the Reset pin hole in its back, etc. Nothing seemed to work.
The player would not turn off. It was recognized by the computer as a USB drive, but attempting to do a firmware update failed. The update utility stated that no player was connected.
I let the player sit unattached to power until it ran down the battery. I then connected it to my computer and formatted it as a USB drive. I then updated the player's firmware using the firmware update application from Sony's web site. The utility stated that I already had the latest firmware, but I could update it anyway.
After the player restarted, it worked again.