OK HDMI loss is a very common issue with modern sets and there is a procedure to follow, the first thing to do is >>try different hdmi products not just one to eliminate the product as the issue then>>
1)Un-plug the set from wall-power wait 5 mins then re-plug back in again try HDMI again
2) If there is a reset to factory default in the settings menu of the TV please use that try the HDMI again
3)If still no go go to the VIZIO website and look for any firmware upgrade for the set under support for your model make sure you have the latest version of firmware.
If all fails then the main-board will need to be replaced (assuming the set is not under warranty) let me know when you get as far as that and I will advise further
If you are not comfortable with the work then you will need a tech www.tvrepairpros.com will locate a tech in your area, hopefully you have some practical ability to carry out work yourself please let me know so I can advise further
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