It is not always the case that the Hard drive has failed. The cause can be shutting the laptop down wrong and corrupting the Data of the drive that is on there. For example all of the files to load the windows operating system.
And example would be if you had a power cut while the laptop was running.
Or if you say pulled the power cord out of the laptop without a battery being in the laptop. Or it shut down unrealistically.
Do you have a windows Install Dvd to put in your dvd drive of the laptop? to re install windows.
If not you should have what is called a recovery DVD ect.