Shin Megami Tensei: Persona 3 Portable

[Maxus]

I tried to play Persona 3 Portable on fullscreen on my laptop. It worked fine yesterday and the days before. But somehow the game's opening wasn't showing while the music itself was playing. Scenes of the opening would come across the (battle and other) transitions.
Today the game's opening is suddenly working normally, but the game began to lag(sound and graphics). I fixed the lags on the normal screen somehow, but when I use the Fullscreen mode , the game or emulator will refuse to unthrottle properly (it will only cause more lag or it won't do anything at all). The controls are lagging , the graphics are lagging , and the sound is lagging.
I tried it out on some of the other games too, but it all ends up the same, lagging sound , graphics and controls and no working speed up.
Anyone else who's got this problem or can anyone help me out?