No one else has tried to answer this, probably because it sounds impossible!! However, I offer a stupid idea...I wonder if your screen goes black whenever you ask the hard drive to operate. When it does so, the electrical load increases and cuts the voltage to your graphics card. Needless to say this should not happen, but may indicate a loose power connection (perhaps you dislodged something when you cleaned your fan) or a failing power supply.
Clutching at straws but worth a thought?