Computer switches itself off

[#1]

During the last couple of days my desktop computer has taken to switching itself off. Its just as thought somebody has switched it off at the plug. It can be switched back on right away and everything appears ok. Yesterday it went off after about 4 hours, then lunchtime today it went off after 20-30 minutes. As I write this it been going for about 45 mins. Is this likely to be a psu problem or would a temperature sensor on the motherboard cause a complete shutdown. The computer is a bit of a hybrid in that I've built it up myself around 4 years ago and added new hard drives and upgraded the motherboard.
Any suggestions would be helpful.
Paul

[#2]

Have you fitted any additional components recently - upgraded anything, added a new disk etc?
Does sound like a PSU failing - this normally happens if it goes over-temp or hits an overload limit and is designed to protect the PSU by shutting itself off as opposed to protecting your PC which it clearly does not do in this situation.
Is the fan in the PSU working?
Maybe look to replace it - and go for a higher spec one as well.
Also check your other fans on CPU/case as sometimes overtemp protection on the mobo may cause a shutoff.

[#3]

Quote from: paulgul

The computer is a bit of a hybrid in that I've built it up myself around 4 years ago and added new hard drives and upgraded the motherboard. Any suggestions would be helpful. Paul

Sounds like it might very well be the PSU struggling then. If you've added more and more, you need to make sure the PSU has a high enough wattage rating to support all the hardware.
Otherwise, if you've got one thats powerful enough, try taking of the processor heatsink and applying some more thermal compound to ensure all the heat is transferred to the heatsink effectively.

[#4]

I suspect as Peter says that your PSU is on the way out.
I dont think it will be the MoBo overheating as it is able to restart immediately.
Normaly if the MoBo has shut itself down it wont start and will give you a series of beebs until it has cooled enough to be safe.

[#5]

Ok, thanks for all the replies,
I haven't added any hardware recently but a lot has been added since I built the computer so it may well be struggling. Since writing the first post I have taken the cover off and given it a good clean inside including the heatsinks, fans and all the vents - it was pretty dusty. It may have been the accumulation of dust just took the temperature over the top. Just have to wait and see. If it still plays up then it looks like a new psu.
paul

[#6]

Hi Paul
I think you have probably cured it. One of My PC's does this kind of thing every few months... I learned the answer is to get the vacuum cleaner out and suck all the dust out of the CPU heat sink. Then it is good as gold until it gets clogged again.
Crevice tools…. You can’t beat them. 

[#7]

The way forward is to take the guess work out of it and install a MB monitor there are loads of FREE ones like
http://www.majorgeeks.com/Motherboard_Monitor_5.3.7.0_Update_2_d5261.html
Most let you log the results so if the pc dies you will be able to see why.
If you do that you will then KNOW if its a heat problem. If the temperature is ok then  its the PSU

[#8]

I used to clear out the dust from my system with a vacuum cleaner. Be carefull though, apparantly vacuum cleaners produce large ammounts of static which could cause severe damage to your components.
Dave

[#9]

They can also suck up the links on the mobo - especially the dysans so be warned!

[#10]

Yup these are sensible warnings... Oh and unplug the PC first as well!
Peter is right you do need to be careful. Personally I dont vacuum mobo components in case I cause damage by knocking them.
Actually I have only ever found I NEEDED to vacuum the heatsink but it makes sense to do the case fans and any case filters while you are in there.
Also if you want to clean the graphics card it is best to take it out first.

[#11]

I have always found a can of air duster, a great way of blowing the dust out of PC cases.
http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=25351&doy=4m8
(But not at that price)
Use it only to blow the worst out, not to leave things spot less, and concentrate on heatsinks.
Take it easy around RAM and any other socketed components, as it can blow dust in between the contacts (I never seen this myself.)
Also keep the can upright, so not to expel the freezing liquid.
Chilly

[#12]

I don't even use that on my heatsink!
I just use a brush and brush the dust out!
The rest of the case is cleaned with a vacuum though... maybe thats why my system has started to cripple itself recently

[#13]

Quote from: God

.... Oh and unplug the PC first as well!

I disagree!
It is a good thing to keep it plugged into the wall socket, so long as it is a switched socket. IE: Switch the socket off, but keep the lead in as you then have the whole thing earthed. (The earth pole isn't switched off when switching a socket).

[#14]

Quote from: samuria

If you do that you will then KNOW if its a heat problem. If the temperature is ok then  its the PSU

What would be a typical running temperature for the cpu and at what sort of temperature would it shut down at.
I've installed the monitor and the cpu temp is now 55 deg C
Paul
Edit:  about 30secs after writing the above the computer shutdown - writing this on the laptop

[#15]

WHAT!  (Readies lightning bolt!)
That is true if there is a switch. On the other hand unless you skid up and down a nylon carpet several times before you stuff a metal vacuum tool against a chip you are unlikely be in trouble. The days of anti-static wrist bands seems to be long gone. Usually earthing yourself before touching the PC is sufficient. But I suppose it is better to be safe than sorry!
Peace be with you okrzynska…