alkore, to start these players can only support a maximum 2GB nand flash memory, if your player is reading 4Gb then it has a memory chip hacked to read as larger than it's true size. Have a read of theis post for some info on this.
http://www.mympxplayer.org/hotmale16...nz-vt2786.html
This is possibly why your player is crashing.
"lattesurf" posted a guide to removing the hack and returning your player to it's true size here:
http://www.mympxplayer.org/how-to-re...ck-vt2400.html
Theming your player depends on your firmware, go to the Settings menu on your player and check the firmware version if it is 9.0.48 or higher then at present there are no tools to backup and theme your player.