Black screen while system is on.

Hello,
Please how do I restore my Dell latitude C600 to start displaying. First, it showed blue screen then I put it OFF. I re-ON it but it went OFF after few minutes by itself. I tried to ON it again and it picked power while the LCD is not displaying. The PC continued to be ON for over hours while the LCD displayed nothing. While this was going on, the PC refused to go OFF except the power supply unit is disconnected. Expecting your reponse. THANK YOU.