It was probably hacked to show 8 Gb, so yes, you have to format it in windows. You can find the real capacity of your player's memory by opening it, on the big chip (samsung or hynix) you'll find a code. Compare it with these ones here
http://s1mp3.org/en/docs_hwspecs.php#flash . Read this too
http://www.mympxplayer.org/1-vt2400....r=asc&&start=0 Good luck