I went to my Acer Aspire SAE380 UD440A PC which was up and running and found that it was off. I checked the outlet, it was good. I checked the power cable-good. I checked the power-on button, it functioned physically with the clicks. I checked the wire connections- intact. I cleaned out the inside, especially the fans, vents and connections. I checked the terminal connections, jacks and plugs- intact. The only things left were the power supply unit itself or maybe it was the little round battery. My power supply failed last year, but it went out little by little, not suddenly off, so I thought maybe it is the little round battery, but I don't have experience observing what happens when that goes out. I don't know whether to look for a new power supply (they are discontinued for this model) and if so is there a compatible one? How can I be sure it's the power supply?