1) Press and hold the 0 (zero) key and at the same time, tap the power button once to switch on your notebook.
2) When the machine Starts beeping; release the 0 key.
3) When prompted by the warning screen; select Yes to continue with the system recovery.
4) Select Recovery of Factory Default Software; click Next.
5) Select Recover to out-of-box state. Click Next again.
7) Click Next to Start recovery.
As nhasian says, if that fails it's a hardware prob. (Try new HDD?)