This happened to my 85 y/o Dad’s Vizio - tried unplugging, rebooting, every troubleshooting tip on line. Input always went back to Smartcast - couldn’t choose any other input! As a last resort - when did you last change batteries in remote - 6 months he says - let’s change them and just see. That worked!!! Able to now select input ‘cable box’ & watch his shows. Thankful as this was stressful over the phone from 600 miles away!