Panasonic Viera TX-P50G30B not coming on: 5 green blinks

Hi, my Panasonic Viera TX-P50G30B won’t come on. When I press the power button, the power light blinks green 5 times and then on the fifth time, it stays on solid green and makes a small click as though it is going to come on, but the screen just stays black. This happened several weeks ago and I have tried leaving it unplugged for ages, pressing the power button and holding it for 60 seconds with the plug unplugged, 20 seconds with it plugged in and on and also 20 seconds with the volume button pressed in too, but to no avail. I am happy to try taking the back off and fixing it, but would be really grateful to have some guidance please.

Many thanks,

Lisa