the Video card is fine, it the external monitor works OK
Your down to the LCD display or the inverter.
Since the inverter is only around 10 -15 dollars I would start with that.
If you shine a light on the LCD screen and can see an image, it narrows the problem to the inverter.
The GPu cable can also cause these kind of symtoms, so removeing the bezel and checking thecable would be a ideal as well.