"Error loading operating system" message

This error means the operating system on the hard disk couldn't load due to possible faulty hard drive or disk controller. The fault could also mean the hard drive needs reseating to make proper connection. Reseat the hard drive and if you still get this error, then you need to determine if the disk controller is faulty.
To do this, remove the hard drive and connect it to an USB hard drive adapter and plug it into a working computer's USB port. If this computer see this hard drive as an external drive and you can also see the contents of the drive, then the hard drive is OK and the fault is a faulty disk controller. If the computer cannot detect the hard drive then the hard drive is faulty.
Then get a new hard drive insert it into youe laptop and install Windows to get your laptop operatioal.