Found this fix that worked for me!
I was having this same issue with my 42" vizio, after contacting vizio through their live chat and following all their trouble shooting steps, this includes using known working cables, one of the ports did start working but not for long, an hour later and it was out again. Thinking this tv wasn't going to get much use with just one hdmi port working I didn't have anything to lose by trying some of my own troubleshooting steps... this is what worked for me, (I remembered doing this on a printer once as a seft test)
1.)Unplug the tv from the wall, unplug the hdmi cables from the back of the tv. Hold the power button down on the tv, keep the power button down on the tv and plug the power cord back into the outlet.
Keep the power button down until the tv turns itself on and then off.
2.)Plug one of the hdmi cables back into the tv, 3.) turn on the tv and the device attached to the other end of the hdmi cable (I used the original cables because they were already behind the walls).
Repeat the last two steps for each hdmi port.
All the hdmi ports are working with the original cables.
Hope this helps someone else. - ahodgson