White Screen Kingdom Heats 2.5 Final Mix

Try launching the KH2 .self file directly using the Boot SELF option and selecting PS3_GAME/USRDIR/kingdom2.self

Also try verifying your disc's integrity

To check if your disc was dumped correctly, you can use PS3-ISO-Rebuilder tool (http://jonnysp.bplaced.net/)
You will need to load a corresponding IRD file, and then your dumped disc folder (JB Folder) or the decrypted ISO.
Wait until all files are checked, everything should be green, counters for missing and corrupted files in the lower left corner should be 0.