My PSP wont load my saved sims2 castaway game-help!?

My PSP wont load my Sims2 castaway saved game. At first I thought it was the game so I got it replaced but still have the same problem, basically every time it tries to load my saved game it switches itself off each time. so i put my memory stick into my brothers psp and tried to load the game and it worked fine. so is it my psp and if so what can I do? All my other games work and load fine so whats wrong. please help! many thanks. x