ADVICE? Dell Dimension 4550 Won't Power On - Blinking PSU & Mobo LED's

Greetings TH forum members :)

I'm totally stumped. The problem I'm experiencing is that if the computer is left unplugged or without a constant power source, the next time you plug it in and try to power it up, it does not respond. The only activity that occurs is the little green LED light on the power supply will blink rapidly; as well as the green LED light on the motherboard, which blinks in tandem with the power supply. I've tried disassembling all the parts, reassembling and reseating everything, to no avail. Tried two separate (compatible) CPU's, two separate sets of RAM, two different HDD's, and even two different GPU's and it does the same thing no matter what's in there. Even swapped the other hardware that was in there already (CPU, RAM, GPU, HDD) to a separate computer to test. All worked fine. The only components that remain constant in each config during testing are the motherboard and PSU... which I suspect either or both are to blame.

Oddly, however - the only thing I find that works is if while the PSU is plugged in to the outlet, if I remove the 20-pin ATX power connector from the motherboard and reinsert it, the machine will power on just fine. The green LED's on the both the motherboard and PSU even turn a solid, persistently glowing green (no blinking). So long as I don't unplug it from the outlet or shut off the surge protector for longer than say - 10 minutes, the computer will fire up just fine every time after that. For all intents and purposes - so long as I do what I mentioned with 20-pin ATX connector before booting it up the first time and leave it plugged in with the "juice" steadily flowing to it - it works perfectly fine; no issues whatsoever (my Dad can even play the games he likes such as City of Heroes, Guild Wars, Half-Life 2, etc.). All parts - including the PSU and motherboard - work as if nothing has happened and just chug right along for hours on end. But as soon as I unplug the computer from the wall socket or shut off the surge protector for more than like 10 minutes, if I go to boot it up - nothing. Just the blinking green LED's on both the Mobo and PSU.

I've even tried moving the little jumper on the motherboard to do a BIOS reset and went as far as replacing the CMOS battery. Nothing. Finally, these particular Dell models have diagnostic LED's on the back I/O panel of the computer. If I've left it unplugged, and the PSU and Mobo are doing the blinking light thing, these diagnostic lights don't even come on at all. No fan spin-up on the PSU or CPU. No other hardware initializes or "winds up". No BIOS post. Blank screen. Nothing. Just the two blinking lights. If I give it a "boost" by removing, then reinserting the 20-pin ATX connector while it's plugged in and start up the computer, all the diagnostic lights (there are 4 altogether), power on and all are green (which means it's reporting no issues).

So.... Any ideas? :( I'm completely lost on this one and I've run out of troubleshooting ideas. My Dad (it's his computer) can simply leave it plugged in at all times, but he usually likes to shut off the surge protector when he's not using the computer (keeps it in the "man-cave" :D). I'm just afraid of the thing having a "short" somewhere (because it's not supposed to behave like that simply because you turn off the main power to the unit) and being a potential fire hazard. Thanks in advance! :)
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  1. I know it's quite a bit to have to read through, but I wanted to ensure I included all the necessary details about what's happening and what I've already tried.

    Does anyone have any general experience with Dell desktops from around the era of the Dimension 4550 that might be able to explain why it may be possible that the PSU and motherboard LED's blink like that and the computer doesn't turn on?

    The thing I find strange is that as long as I sort of "jump start" the PC using the 20-pin ATX connector trick that first time after it's been without power for awhile, everything - including the motherboard and power supply - work just as smoothly as it all has for the roughly 5 or 6 years I've owned the computer before this started happening.
  2. Best answer
    Happened to me turns out that one of the CPU's pins was bent.
  3. Guess failing power supply, do you have another you can try?

    edit: here are your diagnsotic lights:
  4. Best answer selected by revone.
  5. Turns out it was the CPU for me as well. Had one slightly bent pin that I must've overlooked that was causing all the problems. Put another P4 in there (better condition with no bent pins of course), and everything has been perfectly normal ever since. Thanks for pitching in with some guidance, folks =) Much appreciated!
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