PC fails unless PSU turned off/on first

  Kalb 16:47 16 Nov 2007

Press front start switch all fans start but no beebs,no POST. no monitor display ,no WinXP.

Switch off PSU at the back, then on. Press start switch,fans go, one beeb followed by POST, monitor display and Windows loads. Everything works fine.

Windows shuts down normally but won't restart unless you remember to turn off the PSU & then back on before you restart.

Have removed, replaced and changed the Memory & removed and reseated the Graphics card as well as checked all cable connections.
What to do next ?...... any ideas gratefully received

  Pine Man 16:55 16 Nov 2007

I would suspect that your PSU isn't man enough for the job or on it's way out.

I had exactly the same problems and solved it by fitting a larger output PSU. Not a difficult job as long as you remember what goes where!

  Totally-braindead 16:56 16 Nov 2007

Don't know if this could cause it but have you checked the power and reset wires between the switches and the motherboard are the correct way round?
I presume the fans are the case fans and are independent of the motherboard.

  Technotiger 16:57 16 Nov 2007

I agree with Pine Man - PSU needs replacing.

click here

  Pine Man 17:00 16 Nov 2007

Brilliant link - I wish I had had that the first time I changed a PSU!

  Kalb 17:15 16 Nov 2007

Thanks for the responses
Press reset and PC fails to restart unless you turn off the PSU as for a normal start.
Looks like the PSU doesn't it ? At least that's better than something failing on the motherboard
I can't see much of the PSU inside except it is a Jeantech with a number JNP-400P.
Thanks for the link Technotiger

  Totally-braindead 17:18 16 Nov 2007

I would assume the number of the power supply is the clue, I think its probably a 400 watt one.

  Technotiger 17:44 16 Nov 2007

The label with the PSU details will no doubt be on the top of the PSU, so you will have to remove it, at least partially in order to see the details.

  Kalb 17:44 16 Nov 2007

Think you may be right Totally-braindead.
I'm puzzled though because I have just found this link click here and when I add up the power I require its much less than 400 watts...still even a brand new light bulb fails sometimes.
Shall probably try Maplins tomorrow...hope you can still get PSU with 20 pin Mobo connector etc

  FreeCell 20:21 16 Nov 2007

Most power supplies come with the motherboard connector split as 20+4 so that they can be used on older 20 pin mobos.

  Totally-braindead 23:37 16 Nov 2007

Kalb its not just the wattage, its also the stability of the voltage. Cheap or worn out power supplies won't supply a stable current to the 12 volt rail and that can be the cause.

A good quality branded 400 watt power supply will power a lot more than a cheap 400 watt one will before you have problems.

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