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I thought that my CPU fan was gathering too much dust. So I removed it (just the fan), cleaned it and re-attached it.

Now my PC only runs for approximately 15 minutes, then the CPU shuts off. It happens again and again.

What can I do?

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3  
It is likely overheating and you need to figure out why. Is the fan working now? –  uSlackr May 31 '12 at 14:36
    
yeah, the fan working like before, what happened? –  RawR Crew May 31 '12 at 14:38
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Perhaps the heatsink isn't seated correctly causing heat not being able to dissipate. –  superuser May 31 '12 at 14:40
    
Did you plug the fan into the proper port on the motherboard? Some mother boards have CPU and CPU aux 1 and CPU aux 2 4/3 pin connectors right next to each other. –  Kyle May 31 '12 at 14:57
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Watch in the "hardware monitor" section of your bios and write here the temperature of both CPU and motherboard. –  Avio May 31 '12 at 20:02
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4 Answers

up vote 18 down vote accepted

Most CPU fans are attached to a heat sink. The heat sink must make good contact with the CPU, using a good quality heat sink compound. If you only removed the fan without touching the heat sink - the bond should be ok. But it you removed it, without cleaning and applying new heat sink compound, the heat transfer might be poor. A great heat sink compound is Arctic Silver. Other situations to check are that all heat sink attachment legs are properly clicked in place, so that there is no gap between the cpu and heat shield. Usually if the CPU is overheating, the fan speed will increase. But if the bond is majorly off, the fan speed might start max immediately and you wouldn't notice the difference.

There are several free utilities to monitor your CPU temp and Fan speed. Watching these things before it shuts off, should confirm these ideas.

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SpeedFan is one of them. –  avirk May 31 '12 at 15:25
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Let me ask the two obvious questions:

  1. Did you reconnect the wires of the fan?
  2. Did you loosen or move the heat sink while unscrewing the fan?

Both of these can cause a lack of cooling, and modern processors do an emergency shutdown when they overheat.

Finally a bit less obvious: Does the fan still work? Did you clean it with a vacuum cleaner while it was still plugged in? (If you spin it the fan engine become a generator, supplying power to the motherboard which was never intended to receive power on those pins.)

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When the PC shuts itself off, this could be because of a temp over the maximum set in the BIOS for your computer, which thereby causes it to shut off to prevent a fire or damage to the CPU, or other components of the PC.

The Southbridge section of the motherboard is also sensitive to overheating.

The computer power supply can also be the cause of this problem. If it is overheating, it may also shut down the whole PC. Power supplies are closed units, and manufacturers do not recommend disassembling them, because they contain parts which hold a charge and can shock you. If you remove the power supply from the computer, and look inside below the fan, you can often see if the boards are gunked up with pet hair, dust, etc. I have used the pointy end of a small paint brush to dig out the globs of pet hair that build up in my power supply over time. Also, if you DO disassemble your power supply, it will void the warranty most likely.

It may be a worthwhile experience to completely disassemble your PC, and completely blow it out with a low PSI air compressor. Do this outside, in your garage, or another low dust, dry area to avoid damage to your computer.

As other people mentioned, you need to be sure that you have fresh thermal compound on your heat sink, where the sink contacts the cpu itself. If you apply this compound yourself, it ONLY TAKES A DROP for a CPU. I am referring to a normal sized drop, no more! It is supposed to form a THIN layer between the cpu and the heat sink, just enough to fill the gap present.

Finally, be sure that the pins holding the sink to the motherboard are properly placed in their fully inserted position. Some people opt for screw-down mounting for CPU heat sinks, and avoiding the cheap manufacturer push-pin type connectors, for the simple fact that the push-pin system is junk & doesn't work. As you press one corner into place, it pops the opposite corner off, so be sure to push them down into place two at a time, on opposite corners.

Because of excessive amounts of pet hair in my PC, I changed from the heatsink & fan to a closed-loop liquid cooling system. That means that it is sealed, and you never add liquid to the setup. There is a metal block which attaches to the CPU (with the thermal paste, ONE DROP ONLY!), and usually has a small pump inside it. There will be two tubes which feed liquid up to a small radiator, which has a fan attached to it. When it is time to clean out the computer, you just vacuum off the radiator with a normal vacuum hose. This will eliminate the issue of having to clean as often.

Tests have shown that pushing hot air out of the computer & through the radiator actually cools the liquid in the system sufficiently. Whereas pulling room-temperature air into the PC & through the radiator produces less than optimal results, from my personal experience. I think this is because removing warm air from the computer is better than just dumping more air into the case. More air isn't always equal to better cooling, whereas instead removing heat from the computer, will get you the best results. It makes sense if you think about it, less hot air in the computer = a cooler computer.

Also, as previously mentioned there are programs which will tell you the temperature of your CPU, and other components in your computer. One such program is called Speedfan. It is a free application. You NEED TO configure it for your specific motherboard, so do that before expecting useful results.

In closing, it might also be worthwhile to look at the rest of the computers vents. Your CPU fan might be spinning, but not at full speed. Also it might be spinning proper speed, but without any air coming in the front of the machine (because the vents there are clogged with dust, dirt, hair, etc.). If completely removing the side of the computer while you turn it on gets you no better results, then you probably are NOT getting the CPU fan up to a proper speed, or a problem with the contact between the cpu and the heat sink is to blame.

If the PC is on the floor, try putting it in another place, where it gets better airflow. Likewise, if it sits in a corner, it might be getting poor airflow. Is there a heating vent under your desk somewhere? If so, this could be heating your computer up beyond what it is intended to operate as normal temp's. Last but not least, the temperature sensors in the motherboard might be failing also, which could be reporting higher than actual temps, and therefore tripping the thermal protection built into the bios. A thorough cleaning of the computer (as part of a full disassembly process) will uncover a great amount of dust, pet hair, dirt, etc. After each component is removed, and individually cleaned, placed temporarily in a dust-free area, then the case itself can also be cleaned out. I use soft nylon paint brushes to clean fan blades off, and I also use fans with removable blades (enlobal fans by enermax, specifically) and special magnetic bearings for exceptionally long life. Normal fans only lasted me a year or two, these are at 5+ years now, no joke!

I completely disassemble my whole PC annually. I vacuum out the thing monthly. I blow the thing out about 3 times a year. When I blow it out, I use a Kirby vacuum, with the hose attached to the exhaust, and a restrictor placed onto the hose. It's a neat vacuum, but is rather expensive. You can likely find a used one on craigslist or ebay for cheap. Accessories from your local kirby vacuum shop, like new hoses, and a shaft cover, will enable you to use it like I do, as a blower. Be careful using ANYTHING METAL in or around your computer. Things like Kirby's produce a high amount of static electricity, so be sure you have your computer PLUGGED IN using the three pin plug attached to your power supply, and connected to the wall using a 3-pin socket that has an actual ground wire that IS ATTACHED. An electrician can test the third pin on your sockets, to be sure they're in working order. This way, if you do shock your computer, the PSU might take the shock to ground & save your computer.

Just because your fan spins on your CPU cooler, doesn't mean it is spinning at the speed it should be! Your local computer shop can show you a NEW cooler operating at proper speed, which may be spinning much faster than yours, if yours is worn out, old, etc which happens over time & compounded by a dusty or pat-hair laden environment. Happy computing, and I hope this helps.

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Answer SERIOUSLY needs some punctuation and paragraphing –  Journeyman Geek Jun 1 '12 at 8:03
    
Like that @JourneymanGeek? Todd, please include a few paragraphs next time – otherwise people will just skip reading your answer since it's a big wall of text. –  slhck Jun 1 '12 at 16:59
    
Or at the very least add a tl;dr summary to get the solution across quickly until you fix it. Also, when the question/answer is that long, consider breaking it up into sections with headers and horizontal rules, and highlight important parts with italics or bold. Basically, if you must write a novel, use markup to make it readable. ;-) (For the record, it already had punctuation, it was just one massive paragraph; and at least it wasn’t all/no caps.) –  Synetech Jun 2 '12 at 4:49
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I had this problem, but the CPU and GPU temperatures seemed reasonable. I'd recently changed the motherboard, so I wondered if there was a bad connection somewhere. Turns out that one of the "arms" that holds the CPU cooler in place wasn't 100% pressed down, so the CPU must have been operating at too high a temperature when gaming (though the temps didn't seem extreme to me). The computer was fine when I wasn't gaming.

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