Why does my laptop keep restarting?

I have an advent laptop, and whenever pressure is placed on or around the area that the hard drive is on the bottom, for example when I go to lift it up, the whole computer restarts. Often nothing comes up on the screen and it starts up as normal, however sometimes system restore opens. Was just wondering if anyone knew why this happens and if there's anything that I can do to stop it from happening because it's extremely annoying. Thanks