PC won't turn on after testing graphics card in another PC

One of my nephew's PC was giving artifacts on screen and freezes, sometimes not showing anything at all on the monitor even during boot. So I figured that his graphics card was faulty. His system spec:

7300GS graphics
Asus P5LD2-SE motherboard
400W Power supply

Now, his brother had a working PC with system spec:

8800GT graphics
Asus P5N32-e SLI motherboard
550W Power supply

So I took out his 8800GT card to test if it would work in the faulty PC. I installed it into the PCI express slot but there was no 6-pin power cable coming from the power supply. I decided to try my luck and see if it would show any picture on the screen without the additional power cable to the graphics card. When I turned the PC button on, I heard a loud beep sound which I think was coming from the graphics card. There was no picture on the monitor, so I turned the PC off.

Now here's the worse bit. I put the original 8800GT back into the working PC and forgot to plug in the 6-pin power cable and switch the PC on. I heard the same loud beep noise. I turned the PC off and connected the 6-pin power cable to the graphics card and turned the PC on, but PC was DEAD!!!

I can only see the green light on the motherboard, which turns off after about 20 seconds by itself.

I have removed every component other than the motherboard, cpu and ram, power supply but fans do not spin. I have swapped and used different ram. But the problem is same... the motherboard LED does light up and then turns off after 20 seconds. Non of the fans on the system spin. I see no picture on monitor. Nothing is working.

I have tested the power supply in the other PC and its not faulty.

Please help me bringing the 'good' PC back to life. I know the first bad PC needs a new graphics card, but what happened to the second PC t hat was working before swapping graphics??? :(
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  1. did you turn the psu off (and unplug) before plugging in the video card? (either time.) what about when you plugged in the 6 pin? you said you tried to turn the computer on. did you unplug it or turn off the psu before you plugged the 6 pin in?

    were you careful about ESD?
  2. Fail. Dont play no more unless you own the system.
  3. neon neophyte said:
    did you turn the psu off (and unplug) before plugging in the video card? (either time.) what about when you plugged in the 6 pin? you said you tried to turn the computer on. did you unplug it or turn off the psu before you plugged the 6 pin in?

    were you careful about ESD?

    Yes I did turn off the power supply before removing/installing the graphics card. And yes I was careful about removing the electrostatic charge by touching the case before touching the components with my hands.

    Surely, the graphics card wouldn't fail if you forgot to plug the 6-pin power cable and switched PC on. Isn't the whole point of the loud beep to notify you that the power cable to the graphics card isn't plugged in?

    And why would the working PC stop working when I reinsert the graphics card from where it came from?

    I have tried resetting the BIOS using the jumper on the motherboard and removing the battery but didn't work. No sign of life in the PC, other than the green LED on the motherboard, which turns off after 20 seconds (which used to remain lit even when PC was switched off when the PC was working).
  4. no sign of life points towards a broken mobo.

    if it was the graphics card, the computer would still make booting sounds.
  5. Yes, that's what I'm thinking, that it's the motherboard. But I just don't understand why it would fail just like that. All I did was remove graphics and then put it back in, taking obvious precautions.

    Is there anything else I could test to see if its not the motherboard? Maybe there is some shortcircuit somewhere? Is there some protection on the motherboard something like "fuse box" or something that I could check? I'm desperate to get it fixed.
  6. Just to add... I've noticed that there is a very tiny amount of electrical current in the case if I touch certain parts of the case. Other's can't feel the current when they touch, but I certainly can. I sense a very tiny constant vibration if I touch the case softly with my fingertips. Maybe there is a shortcircuit between the case and motherboard somewhere. I will try to build the system outside the case tomorrow and see if the system posts.
  7. Yep, it doesn't take much of a short (or lack of grounding) to stop a system. I've had a PSU save my system from a faulty 4850 before and restarting issues from my comp grounding through the USBs. It doesn't take much.
  8. Well, it looks like motherboard is working. The power supply has failed. At first, the green light was working on the motherboard, but now even that doesn't turn on. I have tested a different power supply and the motherboard green light does turn on. Although short-circuiting the power switch on the motherboard doesn't spin the cpu fan, with everything removed except for the ram and graphics card.)

    Maybe a multiple component failure? Need to do more tests.
  9. Yup. Power supply has failed. Doesn't work in another PC.

    Motherboard gives green LED when you connect it to a working power supply. However, short-circuiting the power pins on motherboard outside of case doesn't spin cpu fan. There seems to be no life in motherboard other than the green LED.

    Graphics card is working now in the first broken PC that I mentioned in original post after connecting 6-pin power cable to it.

    So, is the motherboard fried? Anything I can do to fix it?
  10. OK, here is the final analysis.

    Power supply is dead. Doesn't work in another other PC.

    Motherboard is dead. With a working PSU, it gives green light but no cpu fan or other activity when power switch is pressed (no POST).

    PC was bought in January 2008 with only 1 year warranty.

    What options do I have other than buying a new power supply and a motherboard? Could I get it replaced by the retailer? It was purchased from an online store as a "custom built" where the store built it.
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