Computer won't mirror onto my Samsung 50" plasma TV.

Computer won't mirror onto my Samsung 50" plasma TV.

I have a Samsung 50" plasma that's all I know it is called. I have brought a desktop in hope to mirror it onto the TV. The computer is registering that my TV is connected but the TV just says no signal. I have tried several hdmi cables. At one point the TV did work for a split second but now won't. Does anyone have an answer to why this is. I have also tried in all three hdmi connections on the TV.

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