Computer reboots under load, power supply fan doesn't spin

Barn619 · Apr 10, 2017

Hi. I have a Dell Optiplex 960 mini tower computer that powers off when under too much load and I think the problem is due to overheating and a faulty power supply. Would appreciate feedback/advice.

In troubleshooting I realized that the power supply fan never comes on - not when under a heavy performance load or even when at startup when I first press the power button (and I remember that it i used to hear the fan at power-on). I have two operating systems (Windows 8.1 and Win 10) each on it's own physical drive and the problem occurs on both.

Specs:
Dell Optiplex 960 Mini-Tower
3.15 gigahertz Intel Core Duo Processor
64 kilobyte primary memory cache
6144 kilobyte secondary memory cache
Bus Clock: 1333 megahertz
Video Card: AMD Radeon R5 200 Series
Drive 0: Win 8.1
Drive 1: Win 10
Drive 2: cd-rom
8gb ram
255 watt dell power supply

In the Windows Event Logs I can only find one event related to the power-offs. This event is almost always present after it happens:
Event 41: The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.

I tried two benchmark apps in the troubleshooting process: SpeedFan and OCCT

SpeedFan: (In Windows 8.1) Starting temps before putting system under any significant load

Before Significant Load

Drive 1 44C
Drive 2 35C
Drive 3 35C
GPU 91C
Core 29C
Core 1 29C

Temps just before system powered off

Drive 1 43C
Drive 2 35C
Drive 3 35C
GPU 117C **
Core 52C **
Core 1 46C **

Again, the fan never turned on! Even when the CPU usage was 100% and the temps reached the elevated levels listed above. I'm not a hardware guy. Should the GPU and Core temps reach those levels (117,52,46) without the power supply fan even spinning? And I remember that the power supply fan used to come on regularly.

I tried running the OCCT app in Windows 10 and ran the basic power supply test twice. The system powered off about a minute into the test each time.

Thanks for the feedback!

hang-the-9 · Apr 10, 2017

Yes, bad power supply can do this and the video card is pretty hot. See if the system works fine without the video card in the system.

Really if you think it's a power supply or heat issue, replace the power supply and clean out the system, make sure things are installed well with new thermal paste.

Barn619 · Apr 11, 2017

Thanks for the reply. Per your suggestion I removed the video card (to minimize chance of overheating), connected the monitor to the onboard video and reran the stress tests to induce a performance load. I increased the load until the cpu usage and temps matched the previous levels of the drives and cores when the system used to crash. Without the video card the overall internal temp was upwards of 120C less and I couldn't replicate the overheat/reboot problem. I am convinced that the system should run smooth as long as I can keep it cool. I'm going to order a replacement OEM power supply on ebay and attempt the replacement myself. Will also get some compressed air and clean out the inside.

You mentioned reinstalling internal components with fresh thermal paste. I've never reinstalled a power supply, let alone repaste a cpu (and other components?). Is applying new paste really necessary? I'm not sure I feel comfortable doing it. Can you recommend any resources that could hold me hand as to what to buy and which components need to be pasted?

Thanks!

hang-the-9 · Apr 11, 2017

Barn619 :

Really for that older system I would not spend money or time on trying to get it running. For about $100 you can get a newer Core 2 Quad or even an Intel Core i3 or i3 tower.

Overheating can be caused by old dried up thermal paste and dirty heatsinks/fans so you do want to remove the heatsink on the CPU, clean off the CPU and heatsink, apply new thermal paste and install the heatsink again.

Or just look for a newer used system in your area. Like I said, about $100 and you are done.

Faike · Apr 11, 2017

You can get thermal paste online on Amazon. Just a dab on the CPU and placing the CPU cooler on it will usually spread the paste quite evenly.
There's also sets that come with a spread tool so you can spread out the thermal paste evenly and prevent any bubbles.
Check out amazon for the higher rated thermal pastes, they generally don't run more than 10 bucks.
Replace the power supply by getting another power supply. It's better than frying your board because you aren't sure how to take it apart and clean it out or fix some components. I've watched power supplies literally catch on fire from bad maintenance.
Safer to just get a new one rather than take your PSU apart and check for capacitors, clean it out, then try and put it back together and risk frying your board.
For your CPU it isn't too hard to remove the cooler. Clean it with a microfiber cloth safe for electronics, and clean your CPU itself as well with the cloth, removing any residue of the old thermal paste. If you get the Antec thermal paste set, you can place a large dab on the center and use the spread tool it comes with to evenly spread a layer of thermal paste on the CPU. Some thermal pastes work better by just placing a good dab on it and placing the CPU cooler on it after firmly, preventing bubbles. Just be careful not to rip out your CPU and CPU cooler at the same time which can happen if your thermal paste was pretty bad and there was a bit of dust, as this will damage your CPU permanently. Just carefully jimmy off the CPU cooler.

Your GPU is RUNNING HOT as well. Vacuum or better yet, use a can of compressed air and go crazy on your graphics card. Remove it and blow out all the vents on the card. There's a ton of dust inside of it causing the fans to not spin.
Same with your CPU cooler. And your PSU.

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Computer reboots under load, power supply fan doesn't spin

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