One potential cause of this issue is the use of the HP Sure View Integrated Privacy Screen.
This is a feature from HP which seeks to reduce the risk of information on your screen being seen by others - it drastically reduces the viewing angle the laptop screen can't be view when someone is standing next to you.
The F2 key is an icon with a laptop and checkerboard in the upper left
- Pressing the Fn/Function key and the F2 key should turn this privacy feature on or off
Please see full HP documentation for details: