Computer gone to silicon heaven

[Mouseroo]

Hello,

My trusty old PC has finally (I think) given up, but I just wanted to get some feedback on my diagnosis of the situation.  Here's what happened:
On Tuesday, the PC was absolutely fine.  At the end of the evening, I powered it down as usual - no problems.
When I came to power it up on Wednesday, the fans started whirring, the hard drives were spinning up as normal, but both of my monitors were showing that they were receiving no signal.  So I powered down the PC and powered it up again - exactly the same thing, no signal to either monitor.
My first suspicion at this point was that my graphics card had blown, so I swapped it out for a known working graphics card, but once again, no signal.
So now the only thing I can think of is that it's my motherboard that's the problem.  I know that there's power coming through it (to spin up the drives and fans), but since I'm not seeing anything on-screen, I'm guessing that something in the graphics bus (possibly the AGP slot itself?) has blown.
Does that seem to be a reasonable deduction?
If it is the motherboard, then I might as well replace the CPU, graphics card and RAM at the same time, so I guess the new configuration will be a bit more powerful     That said, I'd rather not spend the money on all that if I don't have to, so if anyone can suggest what else might be causing the problem, then I'd really appreciate it.

Thanks in advance for any information.

Andy

[Rik]

Hi Andy

You've made the elimination test I would have done. Like you, I'd say a mobo fault but...

Have a peer underneath to make sure nothing is touching the case (not likely, but...) and try removing the RAM and subbing it back one or two sticks at a time. If that doesn't help, try unplugging the HDs to see if the PSU is struggling.

[Dangerjunkie]

Hi,

Do you get any beeps when you turn it on? Usually you'd get at least one beep after the RAM check has finished.

My guess would be that your PSU has gone ("I turned it off then it wouldn't turn on again" is a classic for this kind of fault.) It has different voltage lines for different things. The fans and the drive motors run off 12V but the CPU and Mobo mainly run of 3V/5V. If the low voltage output has gone down or is noisy it could very easily stop the machine from booting even though the 12V is there for the big stuff. If you put your ear to the PSU when you turn it on do you hear any strange buzzing or whistling noises?

PSUs are fairly cheap. As long as your machine takes a regular ATX PSU somewhere like Maplin should be able to sort you out with a pretty decent new one for about £20-£30. Do you have another machine you could steal the PSU out of for a test?

Another option is that something in the machine may have failed and could be dragging the PSU down.

Cheers,
Paul.

[Glenn]

I too would say that the PSU is the problem, it has lost it's 5v rail so there is no power to the components on the motherboard.

[Mouseroo]

Hello again,

Thanks to all who have posted information. Here's the story so far:

Have checked for anything making contact with the case - all clear.  Haven't tried re-seating the RAM yet, but did power the PC up to listen out for any BIOS beep notifications, but this time I also had my speakers switched on (something I don't usually do until the PC is booted) and although there were no beeps, I did hear a voice repeating the phrase "System failed CPU check".
Therefore, I'm now thinking that the CPU has failed.  However, if the CPU is driven by one of the lower voltage rails from the PSU, then it may indeed be the PSU which has partially failed.
Unfortunately, I don't have access to another PC which I can swap components out from (I'm currently using my laptop).
Are there any other tests I can perform in order to confirm the PSU and/or CPU failure?

Once again, thanks for any help!   

[Rik]

Got an understanding friend with a working PC? Failing that, put a multimeter across the 5V rail.

[Dangerjunkie]

As Rik says, a multimeter will hopefully find a wrong or absent voltage but won't give an indication of electrical noise on one of the supply rails. Please note that a PSU won't run and produce a voltage unless it is connected to the motherboard (it needs a load and the power button signal from the mobo to run.) Be really careful you only meter between 0V and the rails and you don't short anything together or you will probably kill the PSU and the board/drives if they are still OK.

Good luck,
Paul.

[Mouseroo]

Well, I've got PC owning friends, but I can only imagine their reaction if I asked them to disconnect from World Of Warcraft or Call Of Duty for more than 5 minutes...

I did a quick Google for PSU testers, and I came across this one:

http://www.maplin.co.uk/module.aspx?ModuleNo=45500&doy=29m3

Any comments, reviews or alternative recommendations?
It certainly would seem to be the most cost effective first step.

[Dangerjunkie]

Hi,

I suspect that the 3.3V power rail (the orange wires on the large ATX connector) or maybe the 5V rail (the red wires) has failed or "gone soft" http://pinouts.ru/Power/atx_v2_pinout.shtml (voltages are measured between the black wires and the coloured wires)

That tester will do fine for this machine and other older ones but it won't be good for newer machines that have SATA hard drives as it only has the older white P4 (4 pin) power connector and not the newer flat, black SATA hard drive power connector.

They do the Tester II and the LCD model but those are the same price as a new PSU. The tester you looked at is probably a tool you'll only use once. If it fixes the problem then you will replace the PSU and that will almost certainly outlast the rest of the machine so you won't need the tester again. If it doesn't fix the problem and it turns out to be the mobo you'll be getting a new machine with SATA drives.

How old is the machine?

Cheers,
Paul.

[Mouseroo]

Hi Paul,

Thanks for the info.  The motherboard is 4 or 5 years old now (Asus P4C800-E Deluxe), and the power supply is about 2 years old (Tagan TG480-U01).  The PC does have a couple of SATA drive in it, but I'm happy that the HDDs and fans are getting power - it's the lower voltage rails I'd like to test.
At the moment, the PSU tester I linked to in my previous post seems to be the cheapest option in order to investigate the issue further.  If I do only ever use it once, then I can live with a payout of under £20  (thank goodness there isn't a cheapskate smiley!)

Cheers,
Andy

[Niall]

I had a Tagan PSU a while ago, and while they run they are rock solid stable. Sadly they have a tendency to suddenly die with no warning.