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I have a dual core athlon pc that is refusing to turn on. I had assumed it was the power supply so I've just purchased a new one. But after connecting it up I find that nothing has changed. When I turn on the power, the only sign of life is an led on the ethernet socket that flashes on for half a second. Then nothing - no fan movement either on the PC or the power supply, no beeps, no clunking of hard drives, nothing. My guess is a short circuit somewhere but I am very inexpert on these things. I tried removing a few unused cards to eliminate problems with them but no change. Any suggestions?

I have a multimeter if that helps...

UPDATE: Its alive!... I'm not quite sure what did it as I was plugging so many things in and out... thanks for all the tips.

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Mick: Do us a favor. Backup your files, & report back here in a week that the unplug-plug fix is indeed a permanent fix. I like aking1012's statement: –  Rolnik Nov 22 '10 at 20:20
    
They should have flat tops. <--- Referring to capacitors. I'm going to take a good look at my dead mobo to see if I can spot this symptom. –  Rolnik Nov 22 '10 at 20:21

4 Answers 4

Check for ballooned capacitors...the little cylindrical things on the board. They should have flat tops. If one/some tops are convex, the board is hosed. Failing that remove the board and check behind for pieces of metal that may have fallen behind the board to create the short. Sounds dead, cheaper to buy a new board to me though (for a dual core athlon almost surely cheaper). Think: If I pay myself $10/hr(Wal-Mart wages) for messing with this thing how much am I out before I fix it?

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capacitors are all perfectly flat. The underside of the board looks clean. I take your point about the motherboard... –  Mick Nov 22 '10 at 19:37

Remove everything. Put a towel on a desk, put several pages of newspaper on top of that. Put motherboard on, pull out and reinsert RAM. Connect power supply, connect a hard drive - don't even need video. Power on. Does the hard drive spin up? Do you get error beeps? If so, try connecting video - do you get image? Lots of times the short is a problem with a slot cover or screw shorting motherboard. By removing motherboard from case, we eliminate these as issues. By removing/reinserting RAM, we eliminate a cocked module. By trying without video card, we eliminate that as a problem at first.

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A common error is to connect the main ATX power connector , but forget the supplementary 4-pin one. I once did that myself and got very similar results.

Note that there sometimes are two 4-pin connectors: one with 12V supply for motherboard (black and yellow), and another one with more voltages (black, yellow, orange and red). The first one is connected to separate socket on the motherboard, as on the photo, and the second is used in pair with the main power connector; if the socket on your motherboard is longer than connector on the PSU, you need to plug the second one near the main ATX connector.

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Good point - but I don't think that's the problem. The 4 colour one is not needed. I can tell because there is a kind of plastic stopper blocking the four 4-pin slot immediately next to the main ATX connector. The 2yellow-2black socket is plugged in to a separate 4-pin female socket six inches away. –  Mick Nov 22 '10 at 19:33
    
The 4 pin connector being referred to is NOT directly adjacent to the main ATX connector. While it depends which motherboard you have, look elsewhere for a connector that matches. It will be square, with 4 pins that match one of your power supply outputs, like whitequarks image link. –  hotei Nov 22 '10 at 19:42

Remove all cards, including the graphics card but not the memory. Disconnect all of your drives HDD & CD/DVDROM. The fans should run and you should get as far as hearing the error beeps for a missing graphics card. Post back with the results.

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Still nothing other than the flash by the ethernet socket :-( –  Mick Nov 22 '10 at 19:39

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