Toshiba Satellite M55-S325 turning itself off

Question

My Toshiba Satellite M55-S325 shuts off at will, I thought it was a fan problem,as it was making noise, but I replaced it,I thought it was overheating, as it seemed to cut off more quickly, more as it got hot, or was multi tasking, but now it does it very quickly, even before it boots up, any ideas?ThanksJ