I have a gateway all in one touchscreen, turn it on it starts to power but shuts off, tested power supply it is fine, had another good one so i INSTALLED it still wouldn't power on. Is this a motherboard issue? Cant be the switch because it tries to power on. How would i troubleshoot this further?The problem is with your power regulator if you change the regulator on your mother board every will be as good as new.How many seconds is it on before it shuts off and does the time it stays live vary or always consistent?Only about 2 seconds and it is consistent. Any history not shared yet on what might have DAMAGED it... it was dropped or got wet or a bad storm rolled through or static discharge from finger or did it just one day simply stop working?Posable static discharge, i DIDNT change the power supply myself so who knows what they did, other then that it just one day stopped working. Take it back and demand they fix it properly...

My guess is they swapped in a generic power brick...i would lol but its a friend asking me to fix it, they thought they could do it and they couldnt, i am not experienced in motherboard troubleshooting but i would have at least USED a static MATT when changing the power supply, I wont have time for couple days to mess with it but i am going to try a couple things and post here to see if it worked or not. While you are in there see which PSU is replaced with and look at the Manuf. page to see if it matches...i'll bet a Beer it doesn't.