Sudden shutdown of a fujitsu laptop?

there are occasions wherein the monitor of my laptop will go into pitch black and then the on/off indicator will start blinking. after that i will open my laptop by pressing the on/off button and the next thing that will appear on my laptop is the login window which says under the textbox is that my laptop is in locked mode eventhough i didn't set it because it just suddenly shutdown. sometimes i'm hearing something resembling a lose screw. im not sure yet... there are also occasions wherein my laptop didnt go into pitchblack. what might be the problem?please specify if it is in the hardware or software..and also state the problems and the possible solutions...sorry this laptop is my first so im having difficulty in handling and troubleshooting it..thanks in advance