Narrowing down the bad component in a system that won't power on

Posted on 2006-05-26
Last Modified: 2010-04-25
I have a desktop PC that will not power on -- when I press the Power switch, nothing happens at all -- the fans don't spin, the hard drive doesn't spin up, and even the fan in the power supply doesn't spin.  It's as if the Power switch wasn't connected to the motherboard (but it is).  I am trying to figure out which component needs to be replaced.

Here's the background of how I wound up in this situation:  Last week I was playing with memory timings in the BIOS.  I got too aggressive so the computer wouldn't POST.  I used the jumper on the motherboard to clear the CMOS, but that didn't work.  i tried it many times without success.  Finally, I removed the battery for a few minutes and that didn't help either -- the computer still wouldn't POST.

Then on the advice of a friend, I pulled one stick of RAM out of the mobo (it originally had 2 x 512 of PC3200 RAM).  At that point, with just one stick of 512 MB RAM, the computer POSTed and booted and ran fine.

Then I tried that other stick again:  I put it in slot 2, where it originally was, and the computer wouldn't POST.  I moved it to slot 3, and the computer would POST but wouldn't start Windows.

I figured the RAM was bad, so I ordered a stick of 1 GB to use in slot 1.  It arrived last night, I put it in slot 1, and the PC wouldn't POST.  I moved it to slot 3, and the computer powered up for a few seconds, then I heard a pop, and it died.  

On the theory that the pop was something burning out in the power supply, I replaced it with a brand new OCZ 520 W power supply.  And that takes me back to the first paragraph:  the computer won't power on; it doesn't respond to the Power switch at all.

Since the power supply is brand new, I figure the problem is either the mobo or the actual power switch in the case (maybe it burned out?)  Would anything else prevent the system from powering on?  Could RAM have that effect (I would expect that bad RAM might interfere with POSTing but not with powering on the machine.)

Question by:mitch10021
    LVL 30

    Assisted Solution

    motherboard is it
    LVL 14

    Accepted Solution

    sounds like you shorted the ram & thus the ram socket, the last pop sounds like you blew something on the mobo itself (agree with irwin) & i wouldn't be surprised it you messed up the new 1gb dimm
    LVL 91

    Assisted Solution

    you can test with the old power supply, and test the ram sticks on another mobo.
    I would check the ram slots closely for something shorting in there too.
    a power switch burned out ? hard to believe, since it only shorts 2 pins on the mobo, at max 5V
    you can test it by disconnecting the switch from the mobo, and shorting the 2 pins with a screwdriver for 1 sec
    LVL 30

    Expert Comment

    cool. thank you!

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