unmountable_boot_volume points to a bad or failing hard drive.
It can also be caused by a bad drive controler on the motherboard.
Open the case and check that your drive is properly connected. Unplug and re-plug the power and data cables.
If it's correctly connected, and still can't boot, try installing a new drive, install a fresh copy of windows.
Install the drive into another computer and check that you can access all of it.
If the drive can be accessed in another computer and a new drive don't work in your computer, then, you need to get a new laptop. The drive controller is part of the motherboard and can't be changed.