antoonioo, originally before you did anything to your player, both showed 8GB as there was a memory hack on your player.
Now after you formatted it, the real memory is shown as 128MB (minus about 19MB for player firmware), as the memory hack has been removed in the process.
Also, you have opened up your player to physically check the memory chip's serial number and by checking with Samsung & Hynix's website, the memory chips corresponds to the 128MB.
There is nothing you can do to regain the 8GB, as simply there was never 8GB in your player from the beginning, it was 128MB.
EDIT: You may like to read up these two sticky threads on hacked memory chips by Zaidon:
http://www.mympxplayer.org/viewtopic.php?t=424
and Iridium:
http://www.mympxplayer.org/viewtopic.php?t=839