HP Pavilion 23xi 23-inch black screen but getting power ok

I have a HP Pavilion 23xi 23-inch IPS LED Backlit monitor.

The power light at the bottom right hand corner illuminates white to indicate that the monitor is receiving power but the screen itself remains black.

I have tried using different connections (hmdi, DVI and VGA) but still black screen.

Any ideas. I have taken the stand off and unscrewed the screws at the back but no idea of how to take the back off