Yet another grey screen problem

I have a mid-2012 MacBook Pro running macOS 10.13.3.

On start up the tone sounds, the screen powers up but all I see is a grey/white background, no Apple logo or timer.

I plugged the laptop into my TV using the Mini DisplayPort and I can now see on the external screen that it is booting up normally but nothing is displayed on my laptop except the grey screen.

I've tried various things like rebooting in safe mode, disk repair through OS utilities, resetting NVRAM and resetting the system management controller all of which give the same result when restarting my Mac, unsurprisingly.

Is this problem likely to be caused by physical damage to cables or other components, or could it be a software problem? The built-in camera still works if that means anything.

Thanks all!