Hi asnayagam,
Request you to try following the below steps:
(1) Click on start.
(2) Type “power options” in the search box and hit enter.
(3) Select “balanced” option and click on “change plan settings”.
(4) Now select the “Adjust plan brightness” for “plugged in” option.
(5) Click on save changes.
Check if the display works.
Also you may check if the hot keys work now, if not then you may use the below link and update BIOS and quickset:
http://dell.to/17re4Er Quickset
If you have any other questions do reply to the same thread.