Hello, and sorry you're having problems. We are now connected on this website- which saves you money over having a Tech come to your home, and in many cases we can fix the problem you're having. In other cases, these things do require additional parts to fix. But I can help you with that as well.
There's two possible causes of this problem- the power supply board, or the Mainboard, and unfortunately the only way to narrow it down more beyond an educated guess is to open the TV up and test some voltages using a multi-meter. Do you have any experience measuring voltages and do you have a meter?
Or are you trying to find what the most likely culprit is and a source for the part?
Additionally does the power light consistently have the same response each time you press power?
Can you tell if the screen is consistently backlighting as well each time it's turned on?
The grey is not a backlight, but an image generated by the LCD controller, what we need to tell is if the backlights are lighting the screen up each time the power button is pressed please.
Feel free to reply back if you need more help, or want to reply back with more details. It does not cost you anything more to reply back once you've rated. Please do rate me positively (at least 3 STARS) and I will continue with you until this is sorted. The positive rating ensures I am credited for my work.