Hard Disk Drive Problem Every time computer reboots

Hi!
I would like to ask few things about trouble shooting that is strange with me. They said that if you can see BSOD in your screen, try to shake your tower and eventually your computer will work, is this true? What about the unplugging and reconnecting the power cord if the computer doesn’t turn on. Why do we always have to do this? Is this caused by power supply or the connector? What about the rubbing of the memory? Why do we have to rub it with eraser if you can hear beeps from your computer? Please provide me detailed answer for this
