Chosen Solution

I got a Vizio m420nv lock screen from my local thrift store and it turns on and then within 15 or 20 minutes shuts off automatically by itself is that a specific problem or how do I narrow down what the problem could be

@normaray could be an issue with the power board. you have not told us if it comes back on immediately after it shuts down or if you have to wait. You do want to unplug your set and remove the back to take a look at the power board caps to check for any domed, leaking or otherwise damaged caps (or any other part). Do not touch anything just yet since the caps may still be charged.Post some images of your boards with your question so we can see what you see. Use this guide for that.