PSP tekken 6 iso game black screen?

The game is tekken 6 and its an iso file. first, the game was working fine and all. i have other games which are in iso and cso format also. now, the game just wont start up. its just blank with a black screen. the other games work fine, but whats the problem with this one? ive played some of the story mode and unlocked some of the characters cgi clips and thats all i did in the game. so, what can i do?