Kuronami, Formatting may help but be sure to use the MP3 Player Disk Tool to do it do not format it with windows. You also may not have found the correct firmware yet. For most people who recover their players it is a process of trial and error until they get the right one.
If you open the player and find the board number, the memory chip number and the main processor chip number this information may help you find the firmware version that is for your player.
SK has uploaded some photo's of where you can find this information here
http://www.mympxplayer.com/viewtopic.php?p=1964#1964.