Hi,
Have you checked that the TV was switched to the correct HDMI input?
Have you tried a different (if possible) HDMI input on your TV?
Have you proved that the HDMI input(s) on your TV work by connecting another device with a HDMI connection?
Have you tried a different HDMI cable or proved that the one you are using works, by using it to connect another device to the TV and seeing if it works? (e.g. some mobile phones have mini HDMI outputs)
If the answer to the all the above questions is '''yes''' and given that you have factory restored your tablet, I suggest that you verify that the warranty period on your tablet is still valid and that you contact the manufacturer's customer service section regarding a warranty repair or replacement.