iMac G3 not powering on

I have and old iMac G3 from late 1999, don’t really know anything about the models but i know it’s from that year. When I first bought it everything was working just fine. But just as of a couple of weeks ago, it wouldn’t power on, nothing worked, I tried plugging it in other outlets, I reset the PRAM and replaced the battery, I tested the J7 Connecter and J9 pins, and even checked if there was continuity on the fuse and there was, there was also no light coming from the power button either. But one test that didn’t come back positive was the C4 capacitor, I read that when the iMac is plugged in but not powered on I should get a reading of -1.2 V and when powered on it should jump to +21 V, but I’m getting a reading of barely 0.01 V when powered off and a reading of 6V when powered on, I read that the ground should be this screw

. But even with any other screw on the board it still has the same readings. What does it mean when i’m not getting the correct readings on the C4 capacitor. Another thing I noticed is that when I power on the iMac I can hear what sounds like the the CRT turn on but then flicker off. I don’t know what this means and if it has something to do with the CRT. I tried everything I could and read as much as I could understand, if anyone has any tips to help me out on the problem I would greatly appreciate it. Thank You