Have you attempted to boot it in recovery mode to see if your laptop register's the phone being plugged in? Try that first because if you've never had the S6 plugged in while it's in recovery mode the laptop will start installing the required driver's once it's plugged in the USB port & if the installation complete's then the phone may still be alive! Here's how to boot it in recovery mode...
Galaxy S6 Recovery Mode:
Power Down the Galaxy S6.
Press and Hold the Power Button, Volume Up Button and the Home Buttons at the Same Time.
Continue Holding These Buttons Until You See Some Blue Text at the Top.
When You See the 'Recovery Booting….” ...
Wait Until the Galaxy S6 Fully Boots into the Recovery Mode.