Little life left in system

I got this Power Mac G5 from a guy’s backyard at a tag sale, it was all beat up so i took everything apart, cleaned it, and put it back together. When I plug it in it makes a click sound, and when I press the power button, the LED goes on but immediately turns off as soon as I release it, and it makes no noises whatsoever. It seems to have little signs of life, but I’m still hoping to fix it