PC won't power up

  Ollyolly 21:00 22 Jun 06

My wife works for a small company run by a volunteer management company. One of their PC's won't start so I said I would have a look at it.

When I switch the mains on there is simply no response from the PC. The PSU is quiet and the PSU fan is not running.
I've changed the mains leads, same result.
I've taken the case front cover off to access the on/off switch and however I wiggle that switch about, same result.
I've changed the PSU. Ensured the 20 pin mobo plug was the correct way around, hooked up the hard drive, same result, no power.
There is one lead from the exisiting PSU with a 12 pin plug on it but no socket on the mobo.
I can't think of what else the problem might be.

Any ideas anybody?

  woodchip 21:38 22 Jun 06

How do you know that the PSU you fitted works or is big enough to start the comp? i.e Watts

  Ollyolly 22:04 22 Jun 06

I have tried a PSU from a working PC. The PSU had a smaller in wattage and a 12 pin plug. The 12 pin plug pushed into a socket on the mobo it came from but as I said earlier there is no socket on the problem PC.
I aslo tried a third PSU in the problem PC and got the same result, nothing. This third PSU was 250watt copared with the 300watt original. With only the CPU and HDD to power up I guessed that was enough.

  woodchip 22:08 22 Jun 06

Not enough power. That may be why the other went

  Fruit Bat /\0/\ 22:20 22 Jun 06

I've taken the case front cover off to access the on/off switch and however I wiggle that switch about, same result.

momentarily short the pins on the motherboard where the switch is connected to.

This should signal the PSU to start.

click here
click here

  Ollyolly 22:21 22 Jun 06

Woodchip, thanks for your thoughts.
I'll keep a lookout for one with a higher wattage.
I don't won't to try the one from this PC there is to much attached inside.

  Ollyolly 22:25 22 Jun 06

Fruitbat, thanks for your response.
Bit late now for that sort of thing so I'll digest your post fully and try tomorrow.
I'll let you know how I get on.

  Ollyolly 22:18 23 Jun 06

I traced the on/off switch wires (orange & white)back to the mobo, pulled the connector off the two mobo pins. Switched on the mains power and put a screwdriver across the two pins (end two of an array so it was easy to reach with the driver).
Result - no sound, no power, no flashes, nothing.
I guess that means the on/off switch is not at fault.
I've followed your links and read about shorting pins 14 and 15. Having established the on/off switch is OK I think shorting the pins is the next move. Job done best in daylight with my eyesight. I'll try tomorrow and let you know.

  woodchip 22:22 23 Jun 06

You only have to touch the pins not hold a bridge on them, touching and remove both at same time will start the computer if all else is OK

  Ollyolly 22:38 23 Jun 06

Using the screwdriver I only gave them a quck touch, but no movement from the PSU fan.

  woodchip 22:39 23 Jun 06

PSU def US

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