Computer shuts off, and spazzes in limbo

This is a challenging problem to any computer guru, i really have no answers. All i can say is that randomly- sometimes after several hours, sometimes just a few minutes, while playing a game, browsing, or just listening to music, my computer simply shuts off and stays lit up while making noises as if it were on. The monitor goes black, and the lights on my keyboard and mouse flicker. WAT? The crazy thing is, i thought it was my video card so i took it out- and now it only happens less often! Is it a dying memory module? Is it my psu? Is it the motherboard? Please guys, im running on integrated graphics right now and i cant even watch my movies in fullscreen! I really don't get it. PLEASE help me, my saves are starting to corrupt, and i cant even finish an essay sometimes before something happens! If you do have an answer, give a full explanation. Google hath forsaken me in this case!