Help with a computer shut off problem

[Outrageous]

Normally I'm decent with a computer (I'm not a total noobie) but for the life of me I can't figure out what's wrong with my pc. For a couple weeks now, the power keeps shutting off. I've done and bought a new psu for it, tested all the rams with memtest86 individually to see if memory was the problem. Checked the bios for temps, bought and reapplied new thermal paste to heatsink and processor, reseeded all the connections, but the damn computer keeps powering off (especially during booting). Now and then I can boot into windows (and it's 7, tho I'm pretty sure it's not a software issue) but after a couple minutes, the pc will power off. It's probably time for a new computer (even tho the one giving me trouble is only about 2 yrs old) but thought I should giving asking someone for help a try. So anyone with any ideas?

 

[Outrageous]

Like I said, already replaced the psu with a new one and same problem persists. Fan runs fine.

 

[Willie Boy]

Is it connected to a UPS? Have you checked the outlet it is plugged into?

 

[omminc]

Might be a start up program doing it. I had a problem like that a year or so ago and it was because of a program. If you can, install WinPatrol and disable all start up programs you can slowly check which programs causes the program. If it restarts, it's not a start up program. (reason I say this is because you say it takes some time before it turns off, some start up programs will take time turning on if you have a lot of them.)

Might also want to check the graphic card temp, the fan could be slow or dead unless it's a passive heatsink, then, nvm. Some times upgrading the video driver will cause horrible side effects, try rolling them back if you can.

Before this happed, did you install something new? My webcam did the same thing because the drivers conflicts.

Could also be a short/lose wire somewhere.

Try to do a system restore, that, most of the times, will do the trick.

Not sure otherwise. If I was in your shoes I would re-format it. If it kept on doing it after that, then it's something more serious, like the MoBo, HD, or GFX dieing.

 

[T-Rexx]

The computer shuts down when the motherboard gets the correct shut down code from the software. Because this is digital equipment, the electrical code at its most fundamental level is a series of square waves sent over a line to the motherboard.

I have no idea what the code is, really, but let's just say it is 3 square wave pulses followed by a pause and then 4 more sqaure wave pulses. You are getting electrical interference from some component in your system that is generating so many electrical spikes on the line that, just by the random nature of the pulses, occasionally a sequence comes along that (more or less) matches the shut down code. Then the system shuts down, of course.

The reason you can occasionally boot is that the interference is random. Occasionally, the interference pattern does not have a sequence that mimics the shut down code, and you can boot.

The problem is identifying the component which is generating the interference. If your system has a lot of plug-in cards, you could try leaving the cards out, one at a time, to see if it boots okay without one particular card. But it isn't necessarily a plug-in card. It could be some component on the motherboard which is failing, and generating electrical interference as a result.

Ask trawler what he thinks. He knows about this stuff.

 

[Corny]

are all your cards firm in their slot? is the PSU powerfull enough? swap some cards with older parts from an abandoned computer ... see if you can find a culprit. this is to 80% a hardware issue

 

[trawler69]

I had this problem once and it turned out to be a bunch of smoothing capacitors on the mother board. These are there to add extra smoothing to the power supply in the event of heavy loads. When they go you can get "brown outs" or seemingly random resets. TBH, although these are relatively cheap, it is easier to replace the MB.
Have a look at the attached pic and see if any of your capacitors look like this.

 

[cityboy-stl]

^ That is exactly what happened to me last year. Since the MB was 8 years old it was time to replace it anyway....but, what causes this? Are the capacitors defective or do they "just do that" after a while?

 

[trawler69]

Electrolytic capacitors have a limited life and this can be greatly decreased by overheating, also these are high value low voltage ones with large surface area and very thin dielectric layer which makes them more prone to fail. I have heard it reported that some can have a contaminated electrolyte that can cause a gas build up which leads to rupturing of the can. This is why they have the built in weak spots (the scored lines on the top of the can) They didn't used to have these and when they went they would go with a bang. I once had one fly though a closed window when I was young. Most impressive!