Why is my TV stuck on a blank screen after turning on?

Why is my TV stuck on a blank screen after turning on?

My LG TV (model 49uh6100) backlight was purple so I changed them all out with new LED strips. Now when I turn the TV on the backlight kicks on but I don't have any picture at all.I have triple checked all of my connections and replaced the main board and the t-con board but I have no picture at all. Not even the LG logo comes on when I turn the TV on.

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