PC switches off during start up

  Jem 08:07 16 Dec 2010

I have a 5 year old (Evesham) PC which has suddenly developed a strange problem. Symptoms are:

When booting up from having been shutdown overnight it will suddenly switch itself off around 45 seconds into the start up.

The light that flashes during normal computer activity (indicating hard disk activity?) will then flash on and off quite slowly and the PC will not respond at all when I press the start up button. There is nothing on the screen.

I then switch off at mains and after around 45 seconds the light on front eventually stops flashing. I then switch mains power back on and the PC will start up normally (except it has a warning message reporting an abnormal shutdown asking if I want to start Windows normally).

The PC will then appear to run normally all day.

I am mystified. It doesn't look like a heating problem and I haven't loaded new hardware (or software) recently. Any ideas?

  gengiscant 08:24 16 Dec 2010

After 5 years I think a bit of a service is called for, this will involve removing certain components and re-seating them.

I would imagine a fair amount of dust is lurking so a soft clean brush, I use a reasonable quality paintbrush which has been thoroughly worked to remove any loose hairs, a vacuum cleaner is useful here also. making sure you give all fans,including the one in the power supply a thorough clean.

I would remove the heat sink from the CPU and clean off the old thermal paste, I use a dab of aftershave on a clean lint free cloth, then apply a very thin layer of the thermal paste.

I would also check that all cables are firmly seated, remove and re-seat if unsure.

Post back if you still have your problem.

  Jem 18:18 16 Dec 2010

Thanks for your helpful suggestions. I have vacuumed out dust quite a few times over the years and will do so again. Removing and reseating components sounds a bit more risky but will try that if no improvements. Do I need to reseat memory cards? They always seem rather fragile.

Any ideas on why this only seems to happen on first start up from cold?

  gengiscant 08:52 17 Dec 2010

'Removing and reseating components sounds a bit more risky' I promise you it is a simple process.

Make sure your power supply fan is clean, it could be that your PSU is failing. But I tend to feel that it is a possible heat problem. Which is why I suggested removing your heat-sink from your chip and renewing the thermal paste.

Obviously it is a bit of a hit and miss affair trying to diagnose a problem such as yours via a forum, I am just going through some of the steps I might do if I had a similar problem.

  Jem 09:27 22 Dec 2010

An update and more info. Have unplugged and replugged all the cards inside and thoroughly cleaned everything. Have not yet unplugged processor because symptoms do not seem to me to be consistent with overheating.

I.e. The PC only exhibits this switch off problem in first start up from cold. Once it is running it will continue for 12 hours without problem.

Also, the switch off always happens at the same point in the start up sequence. It goes through the initial Bios screens, then the screen with the Windows XP logo and bars moving left to right; the screen then goes blank (as normal) just before it is about to change to blue and show the "Windows is starting up" message. It is just prior to this switch to the blue screen that the PC switches off. If I start it up in "Safe Mode" it will almost always start up without switch off and then when I "Restart" into normal mode it will start up OK.

My theory is that this could be the Power Supply (when cold) not quite coping with the demands of hardware when different components (disk drives, graphics cards etc. are starting at a particular point in the start up. Perhaps when the power supply is warmed up it's OK?

When the switch off occurs the motherboard light flashes slowly and the only way to restart is to switch off at mains and wait 45 seconds for this light to stop.

Any ideas on this behaviour very welcome!

  lotvic 09:50 22 Dec 2010

Prior to switching off at mains it is best to first interrupt pc's startup, switch off by holding in the power button on tower for about 10 seconds, this is a more gentle on your harddrive than a sudden power cutoff.

  Jem 10:31 22 Dec 2010


I think you have misunderstood the problem. I don't switch the PC off. The PC switches itself off. All action stops instantly (just like a power cut) with fans stopping etc.

I only switch off at mains after this has happened because it will not respond to any attempt to restart if I do not do this. Pressing the button does nothing; even holding the button in (which normally switches everything off. The motherboard front light just flashes slowly and continues to do so for 45 secs even with the mains power off. Only when this light finally stops flashing can I re-start.

  lotvic 10:37 22 Dec 2010

Jem, you're right I did, sorry.... :(

  gengiscant 12:14 22 Dec 2010

Perhaps your PSU is failing and as you say that as more and more components are coming on line the PSU is having difficulties.
What wattage is your PSU?

  Jem 13:47 27 Dec 2010


I have an update. My exiting PSU is the original one and is 300W. I bought a new Antec 650W PSU and fitted it this morning. Unfortunately it made no difference. All the same symptoms with the computer instantly losing all power (ie instant collapse, fans stop, blank screen).

The fault occurs virtually every time PC statrst up from cold at the point when the "black Windows XP" screen is about to switch to the blue background "Windows is starting up" screen. If the PC gets beyond this point it works for hours without problem. However, it has now very occasionally done the "sudden switch off" when I try to open a new web page some hours into use - but this is rare.

I'm really at a loss to know what to try next!

  Jem 15:08 27 Dec 2010

Just one further question:

In order to try to isolate any fault would it be a good idea to disconnect the other disk drives (I have a C:drive plus 2 further internal drives for data)? If so, can I just remove the power cables to each to do this?

Also is it worth trying a "System Restore" to a round a month ago before the fault started?

My feeling is the PC is getting steadily more unreliable (i.e. the symptoms are getting worse) so it may be a degrading component?

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