How old is this TV? LCD based TVs (as almost all are today except for OLED) require a backlight. This is provided either by a florescent light or an array of LED lights (either along the edge or directly behind the screen). If that light fails, then you can't see the image. Replacing such a light is not something a typical user can do themselves. If the TV is still under warranty, you can probably get it repaired. If not, the cost to repair might get very close to the price of a new TV. Only you can determine which makes more sense for you.
Dan
Roku Community Streaming Expert
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