Hi,
Here is a link to the Win 8.1 drivers for your laptop.
Select Bluetooth and Modem in the ''Component ''box on the page and then download the BT drivers and install them in your laptop.
Only download the BT drivers at this stage. Once you have fixed the BT problem you can go on and see what else needs to be fixed.
http://support.lenovo.com/au/en/products/Laptops-and-netbooks/Lenovo-G-Series-laptops/G40-70-Notebook-Lenovo?tabName=Downloads&linkTrack=Mast:SubNav:Support:Drivers%20and%20Software