OOO8662 , your player would be using the v3.5.xx series firmwares.
v3.5.35 here
http://www.mympxplayer.org/actions-3535-dc15.html
v3.5.37 here
http://www.mympxplayer.org/actions-3537-dc16.html
As there is no way of telling which firmware would work properly with your player, you will need to try all of those for your screen size, one by one.
Also, the Hynix HY27UGO82G2M is a 2Gigabit (256MegaByte) memory chip. Which means that your player was a hacked 256MB to show 512MB.