Screen was working fine but now suddely black? HDMI fine

I have installed Mountain Lion on to my Ivy Bridge 4540.

I has been working fine for a week now.
Last night I shut it down normally and closed the lid. This morning on pressing the power button is makes a few internal processor sounds (the usual stuff) but the screen stays black.
I searched around for answers and have tried re-seating the ram chips, doing the reset thing with power and battery removed etc but nothing changed.
If I press the volume up and down button I can hear sound so the machine is working.
I have just plugged in the HDMI and I can now view the fully working desktop on my TV so thats all fine.

I'm a bit stuck now! I have been searching the internet all day for answers but every thread I find is with people who have got a black screen from the start where as mine has been working fine.

I will mention that when I first bought this laptop second hand it the screen was black as well but I left it plugged in overnight and it booted into windows just fine in the morning.

Any ideas, maybe a problem with the screen it's self? If so that would be perfect as I am about to do a screen upgrade once the new panel arrives. But I'm just worried it's something else.

Right, latest update:

I just removed the back to have a little look around.
The wires to the wifi card (old one that is not compatible) looked a bit twisted although seems to be connected ok so I re-routed those and closed it back up.
Removed the battery and held the power button for 15 seconds again.

Now it has booted up and the internal screen is working again!?!?!?
So the mystery thickens. Any clues although it's sounding more like a problem with the screen it's self to me. Saying that I am not a computer wizard on the programming side if things.