Debbie, According to the forum below, the power supply board contains the high voltage inverters, the biggest load on the power supply and will be the faulty power supply board that's causing the screeching and shutting down. There was also a recall on your model a few years ago. Check the attached links,instruction and guides, Good luck
I hope this helped you out, if so let me know by pressing the helpful button.
http://www.justanswer.com/tv-repair/8owl6-60-vizio-smart-tv-e601i-a3-and.html
http://hdguru.com/vizio-issues-a-recall-on-large-screen-led-lcd-hdtvs/