PC Restarts For No Apparant Reason

[Laguna]

This problem has only started today. I was listening to a selection of songs while not at my PC. Halfway through one of the songs, the music stopped so I went to see what had happened. I turned the monitor on and it was in the process of restarting and was at the Windows Loading Screen. When it rebooted there was no error at all.

Then just a few moments ago, I had Firefox open, I minimised it so that I could change the song that I was listening to and after a few seconds of the new song being played the PC restarted, no blue screen, no error of any kind. It has loaded up fine with no indication of what happened at all.

I use Windows Media Player 10, and the PC is fairly new, ie less than two years old.

Any ideas what could have caused these reboots?

[jlreich]

PSU would be my first thought, if the CPU is not overheating.

Although I was cleaning some malware from a customers machine last week, it was doing the same thing, just shutting off for no apparent reason. No BSOD, no nothing... The "star field" screen saver would also freeze, although it would come out of the screen saver when I moved the mouse.

Tested the PSU it was fine, tested it under load, it was fine.

Got rid of a some of viruses and it doesn't do it anymore. :confused: No restarts, no screen saver freezes.

Not saying your are infected, just noting something I thought was very curious.

[Laguna]

My initial thoughts were of a software clash, not malware, but possibly Media Player acting up?

Are there any diagnostics you would recommend running? The PSU is a 500W one, and there is no chance that it is being strained, so even still is there a possibility that it is on the way out? It's only a recent problem, I mean it literally only started about 4 or 5 hours ago and has happened twice.

[OrbitzXT]

I'm not as technical as many of the people here but I like to do a reinstall anytime anything goes wrong. I mainly am a gamer so data isnt a concern for me. If that doesn't fix your problem then I would seek out other causes. Interestingly I had the same issue as you, but the cause of my problem was the sound card wasn't fully seated in the PCI slot. All my parts except my case came and I had assembled it on cardboard so the cardboard pushed it out.

[mjc]

Yeah, there is a chance of the PSU crapping out...

Usually, when it does it suddenly, with no error evident the problem is heat or power related...but not always.

[Laguna]

What else could it be? And how can I check if it is the PSU on the way out? Are there any diagnostics I could run to find out? On the subject of heat, I have 5 fans overall all running at all times (the PSU has 2), so does that rule out a heat problem?

[jlreich]

What else could it be? And how can I check if it is the PSU on the way out?
I usually use a multimeter. While the computer is running I use a free 4pin molex connectors, stick the ground lead in one of the pins with a black wire, stick the red lead in the pin with a red wire(5v) and the yellow wire (12v), one at a time of course. Then startup a program to load the PSU and see how the voltages are doing. If they are dropping or rising 10% above or below what they should be, then it's time to RMA or go shopping. Personally I like to see no more than 5%.

You will most likely see some fluctuation when under load, but I usually see no more than a tenth of a volt difference in the 12v rail, and a few hundredths in the 5v rail, even less the higher quality the PSU is.

Do not try this if you are afraid of getting shocked or frying your system. Be careful not to cross the leads of the multimeter as it will short out your system and possibly shock the crap out of you.

I have 5 fans overall all running at all times (the PSU has 2), so does that rule out a heat problem?
Not necessarily. If the HSF is not on right or has gotten knocked around, or the thermal compound is wearing out, or the CPU fan is not working or working at full capacity, then the case fans won't make much difference.

But usually on a modern system you will hear a warning siren if the CPU is overheating to the point of shutting down. Assuming you have a working mobo speaker, and have overheating protection enabled in the BIOS.

Make sure you have "automatically restart" upon system failure is unchecked. My computer> r-click> properties> advanced tab> startup and recovery settings.

If it's a windows problem it should blue screen and give an error message.

[Laguna]

OK, I decided to run a MemTest, and it shut down (not restart) during it. When it did I couldn't turn it back on. I unplugged it and plugged it back in again and I was then able to turn it back on. So does that prove anything?

[jlreich]

Do you have a spare PSU to try in it?

It's possible it's the ram, but ram will usually create errors and not shut the whole system down. Do you have a spare stick of ram to try? Or try one stick at a time if you have more than one stick.

How are the temps in BIOS?

Is the fan on the PSU turning like it should be? How hot does the air coming out of the PSU feel? It should feel fairly warm, but not hot.

[Laguna]

Air coming from the PSU feels cool right now but I'm only after turning the machine on so we'll wait and see.

I don't have a spare PSU at the moment, but I do have two sticks of RAM in the machine so I'll try taking one out at a time and see if that helps.
But I agree with you when you say usually when it's the RAM you get errors and the machine doesn't shut down as I have dealt with other peoples RAM issues before.

I was planning on making a new machine soon anyway, but I was still planning on having this one running so I need to have it fixed either way.
I think I'll monitor the machine's behaviour over the next few days and take it from there.

I might even take the machine apart completely again and re-assemble it making sure all is well and fully in place.

[Laguna]

Well I put a different PSU in yesterday and the problem has completely stopped.
Just as I changed them I noticed that on the power to the motherboard the connector was just ever so slightly loose, I changed the PSU anyway but I still plan on re-connecting the other PSU to see if it works at some point.

Thanks for your help jlreich.

[jlreich]

Great! Glad you got it figured out. :cool:

I was definitely leaning towards the PSU being the culprit. Typical symptoms, although there are other things that can do it as well.

If you find out the other PSU is indeed good, keep it around for a backup and testing. Good PSU's being so expensive is the reasons I hate telling people their PSU is probably dying and try to go through a lot of other testing to rule out less expensive components first. But if you have a known good one around to swap in, then you know you are not wasting the cash on a new one. :)

And a lot of people have no idea how to use a multimeter. I don't really trust the PSU testers all that much, and you can't test under load to see how it is performing with a good pull on it.

[Laguna]

I just remembered I had one I had taken out of a different machine that I sold.
Anyway just posting back (a tad late I know) to say thanks again for all your help.

I will definitely be checking the other PSU out again at a later date,
I had to sacrifice 100W so I'm down to 400W:)

Only thing bothering me now is that I had to cut all the cable ties I originally had in place so now my Wires are all over the place in there!!
Which unfortunately I can see through the side window on the case.:D