Dead Gateway

I have a Gateway desktop (older model) has Windows 2000. Our electric flickered one night and now it won’t come on. The button on the front that is usually green when it’s on is no yellow. I openned up the case and when the power button is pressed NO fans turn, it is completely dead. I replaced the power supply and now when the power button is pressed, ALL fans start to turn like it’s going to come on but then they all stop and the button on the front stays yellow.
Need HELP !