If there is a risk of losing important data, the most important thing at this stage is NOT TO OVERWRITE THE FILES!
Do NOT attempt to repair or re-install the O/S unless you are 100% certain of what you are doing.
You may not be able to boot from the disk, but you may still be able to read the data areas. Of course, you may run into problems with NTFS permissions, if it was an NTFS volume.
You can check the existing disk by taking it out of the laptop and either plugging it into a USB caddy, or connecting it via a converter onto an IDE channel on a desktop PC.
My suggestion in this situation is to buy a replacement hard disk, together with a USB caddy that will fit the hard disk.
Then remove the existing disk, install the replacement and make a fresh install of the O/S. Once the laptop is up and running, connect the old disk into the USB caddy and extract the data from it - assuming you can.
SD