I had a simular issue but I was on the phone when a second call came in, and I tried to answer the incoming call and the phone screen went blank but I could hear the caller through the speaker phone. I hit the power switch thinking my screen lock came on and the phone at that point went dead. I took it to a sprint repair center and they could not get to power up and opened the case and felt the battery was toast. They ordered me a new phone and when it came in they swapped the battery in to my old phone to see if I could recover some data I needed and the phone still would not power on. I have had that new phone now for less than two weeks and today I got into my car and plugged it into my car charger and started WAZE my navi app and the phone went dead. I pushed the power button and got the LG logo for a few seconds then a picture of a battery on the screen that is blue in color and shows a lightning bolt inside the battery icon. That icon stays on the screen until I push the power button then the battery icon goes away and the green light at the top of the screen is a slow on and off blinking. I have no Idea what to try at this point. I think my battery was at or nearly fully charged when I plugged it in. BTW stock phone no rooting or anything.