Mother board wont power up. PSU is Fine. Motherboard is also fine.

I'm having a hard time fixing this computer. There are a few things I know for sure, The things I don't know are obviously what is keeping it from working haha.
I have a computer that one day wouldn't boot up.
I thought it might be the power supply because an old dell 250 w powered the motherboard and fans.
I bought a new power supply and it didn't work. I thought it was bad so I exchanged it for a new one.
The new one also did not work.
Out of curiosity I tried it in an old spare parts dell.
The PSU I bought worked. The 250w PSU worked. And the original PSU I thought was bad worked.
It can't be the power supply because they all work in the old computer.
I also don't think its the motherboard because the 250 w worked in the computer that wont get power.
I've used an Antec 500w and a TX 650w. The original PSU is a Rosewill 500w.
I've taken everything out of the case, blew everything off with dust off and carefully put everything back in to try to make sure everything was grounded and mounted properly.
If you have any ideas for me to try or you know whats wrong please let me know.
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  1. Have you gone through the boot problems sticky in homebuilt? I guess it is more for newly built PCs, but it could offer some ideas for your case. Look more near the bottom.
  2. I took a look at that. I have done everything but try the ram cards in different slots. That shouldn't really matter too much though. The weird thing is that the computer will boot up just fine on the dell 250W power supply but it wouldn't with any other power supplies. but they all worked in my old dell tower. I know the power supplies were good cause they're brand new and I know the motherboard is capable of getting power because of the 250w psu. It's really confusing.
  3. You do realise don’t you that Dell power supplies are non standard? If your computer was powered by a Dell power supply originally then fitting a standard power supply won’t work. The pin outs on the 20 pin connector are different so you need to get a Dell power supply if you want your computer to work.
  4. I know. And I could care less if the POS Dell ran or not haha. I have a custom built PC that needs the power supply. The only PSU that will make the custom built turn any fans or put on lights is the dell PSU. It is not a Dell motherboard. I have a dell that just sits around and is partially in pieces. I tested all the PSU's that I bought/exchanged in the dell pc to see if they worked. They all powered the dell computer. None of them however, would give any power to the Custom built. The original powersupply that was in the custom built is a rosewill 500w. It no longer works in the custom built. But it will power the dell. This made me think it was the motherboard. But, the dell PSU will power the custom built computer. it is only 250 w though and does not have the video card 6 pin connector.
  5. Fitting a Dell power supply to a standard motherboard would blow up the motherboard if it were to start up also fitting a standard power supply to a Dell motherboard would blow up the motherboard if it were to start up. In practice the power supply does not start up when connected to the wrong type of motherboard.
    If you connected the Dell power supply to your standard motherboard and it started up then for sure you have blown up your motherboard and maybe other parts as well.
  6. pjm, the newer Dell systems conform to the ATX standard on pinouts. They have for several years.

    imnicuhtine said:
    I took a look at that.

    I mean work through, not just read over it. Have you tried breadboarding?

    Breadboard - that isolates any kind of case problem.
    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.
    You do have a case speaker installed, right? If not, you really, really need one. If you case or motherboard didn't come with a system speaker you can buy one here:

    With just motherboard, CPU & HSF, case speaker, and PSU; when you boot, you should hear a series of long beeps indicating memory problems.

    Silence here indicates a problem with (in most likely order) the PSU, motherboard, or very rarely the CPU.

    If you hear the beeps, add one memory stick. The beep pattern should change to one long and two or three short indicating missing video. Continuous beeps or silence indicate problems with the memory. Test each memory stick separately, then all together. Keep in mind that the memory test routines in the BIOS are very rudimentary.

    Add the video card. The beep pattern should change to the single short beep of a successful POST.
    NOTE: You do not need drives, keyboard, mouse, or monitor for a successful POST.

    As you move through the testing, I recommend that you take notes and keep track of part numbers and if you need to, serial numbers. It's embarasing to move parts around, change the symptoms, and realize that you lost track of what you did. (Don't ask me how I know this. :))
  7. Yeah i've preety much done that. Except it was in the case. I only plugged in the 24 pin to the motherboard to see if i could get my case fans to run and also the fan over the heat sink over my cpu. None of the fans would even budge, and no led's by the start button would come on either with any of the power supplies that i bought. The only psu that would give any sign of power was the 250w dell psu. it would make the fans start turning and the led's come on. but when the psu's were plugged into the custom built computer, i would hit the power button on the computer and absolutely nothing would happen.
  8. thanks for the advice guys i appreciate it.
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