I have a Toshiba Satellite L455-S5975 Laptop Computer that is not functioning properly. When I try to turn it on, it only gets as far as a black screen with a flashing cursor in the upper left hand corner. I have tried to recover it but still I only get to the black screen with the blinking cursor in the upper left hand corner of the screen. What is the problem and how can I correct it ? It is Windows 7 Home Premium 32 Bit.