Dear All,
* Press Fn+F5 or Fn+F6 simultaneously while notebook is turn on
* if display switching not works just connect your laptop to external display and re-start (press and hold the power key until power LED goes off. after couple of seconds press power key again) and check any visuals on external display
* if you can see any visuals on External display, you should check the internal display and Flex cable and connector as well
* Open the cover of RAM slots and remove RAMs safely, clean the RAM interfaces, reinstall RANs safely and try to boot normally
* onc of above step not works for you, its time for advanced level repair to check the GPU output and and CPU clocks and Bus (Board level repair)