: Once the standby light begins to flash rapidly or an "Upgrading" screen appears, release the button. Do not turn off the TV during this process.
Do you have the (often printed on the green PCB) to double-check this firmware's compatibility? How to Update Your Vizio TV Software Download MS3458 U801 3840x2160 Vios TV49174K rar
: Ensure the file is named correctly (usually MstarUpgrade.bin or similar) and that you are using a USB 2.0 port if available. : Once the standby light begins to flash