Thank you for checking.
So the remote(s) are fine.
This then also unfortunately means that it is a hardware problem in the tv, a fault sensor board or control board.
This issue could be a manufacturing defect, but is also often caused by a power event (shock/surge, prolonged over/under voltage condition, etc).
This could also be the result of age related wear and tear; These vizio tvs are built for a low price point, not for quality. It is typical for them to last just a few years at best. I didn't see an actual model number, but based on the size you indicated I would estimate it is at least 5 years old.
There is one step you can take here, both as a possible fix, as well as a diagnostic evaluation:
1) Unplug the power cord from the outlet
2) Wait at least 1 hour (60+ Minutes)
3) Press and hold the power button (on the set, not the remote) for 60 seconds
4) Keep holding power button while plugging back in, and for another 60 seconds after. When plugging back in, go directly to the wall outlet, bypassing any power strips or surge protectors.
If this reset process does not work, it would unfortunately confirm an internal hardware failure.
This is something that would require repairs to correct; if you're thinking about a do it yourself repair, you'll need to be comfortable and skilled with electronics repairs, which could include dismantling the set (removing the back panel of the tv), diagnostics testing with a multimeter, changing out boards as needed, and possibly desoldering/removing and soldering/replacing individual components.
If you’re considering repair at a local shop, you’ll find a typical repair to be around $300 for diagnostics, parts, and labor.
For a tv of this size/brand however, replacement will make more sense. You can get a brand new LED tv with a fresh warranty, from a more reputable brand, in the under $300 range.
I can help you with finding parts, finding a repair shop, or recommending replacement options, if desired.
My apologies for the news.