If the keyboard isn't working, chances are the keyboard is already damaged and needs to be replaced already. Here are also some troubleshooting steps that may help.
- Start by uninstalling/reinstalling the keyboard driver.
- Open Device Manager and uninstall the keyboard driver.
- Reboot the laptop once completely uninstalled and it should reinstall the driver automatically.
- After the reboot do test it again and see if the same problem will persist or not.
- If it will still not work, do try an external USB keyboard and see if the backspace button will work or not.
- If the backspace will work normally onto the USB keyboard that means the entire keyboard needs to be replaced.