I have an old Dell XPS 420 desktop that wouldn't come on some weeks ago. I was finally able to get it working by cutting the green wire connecting the power supply to motherboard and then using a switch to ground the green wire (on the power supply side) to ground and then pressing the front power button on the desktop.
Five days ago, even the switch workaround failed and the unit failed to come on.
First thing I did was remove all the cards within (video card, USB 3 card, etc). Still no power up. I then decided to unplug the large 24 pin connector from power supply to motherboard and, when I grounded the power supply green wire, the power supply came on and I believe all the SSD drives did too as I didn't disconnect those. I decided to try opening the front DVD drive and it opened right up electronically. So, the power supply was now working as long as the 24 pin connector was unplugged from the motherboard.
I'm not sure, but it seems to me like there is a short on the motherboard somewhere, since the power supply won't start when the 24 pin connector is plugged in.
Tonight, after plugging back in the 24 pin connector, I decided to keep flipping the external toggle switch to ground while noting whether or not the power supply would start and the blue light would illuminate. Much to my surprise, it finally did, I depressed the front blue illuminated power button and the PC booted up. In fact, I am sending this message from it now.
Now I'm not sure whether I want to turn it off again for fear I'll be back to no power up. Any idea what could be causing what appears to be an intermittent no power up issue? Can we rule out the power supply since it seems to activate if not plugging in the 24 pin connector (but it is now)?
Any ideas would be welcome. This old 2008 desktop is my workhorse and I am basically lost without it. My PC and Internet demands are light, so that's why I am still able to use it. There are a lot of electrolytics on the motherboard and I understand that those fail with age and can cause a short. I do have an electrolytic tester, but I'd have to remove the motherboard to access the caps and it won't be easy. If that's even what could be wrong.
Thanks in advance for any help.