My G4 dual 500 won't power-up. I push the power button and nada. I've reset the PMU. I've left it unplugged then reset the PMU. The battery is only a couple years old. I've removed the battery, left it for days, also unplugged it. Nothing seems to work. Is it the power-supply?
Yes. It's the power supply. If you press the power button and get a quick blue flash from the power switch, your power supply is usually OK. In that case, reseting the PMU will work or you have a bad logic board. If you press the power button and as you say "nada," that's a power supply. If you do decide to replace the power supply, be sure to get the exact right one. Some similar models do not share the same PS. Buying the wrong one and installing it will be a bad test.