My tv back light isn't working 55put4900/12 Philip's 55 4k

My tv back light isn't working 55put4900/12 Philip's 55 4k

I've just gone to turn the tv on and no picture just a black screen but has power if I turn the light out I can see the menu very slightly and it's on and off for a couple of seconds flashing . It's a Philip's 55 4k 2 and a half years old model number 55put4900/12

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