Black screen while GPU fans rotate at max speed. I want to know if my 750 Watt PSU is the cause of this problem.

Sorry if it's long, I will try to keep it short and readable.

Problem: Occasional black screen with GPU fans at max speed. Only happened since I installed new Scythe Mugen 4 CPU fan (160 Watt). Happened one or two times two weeks ago, auto resolved by waiting then just starting PC again. Two days ago it happened again, but the computer wouldn't start anymore until I 'fixed' it. After I thought I 'fixed' it, it happened again today. Although it was much more easily fixed this time.

Potential causes: Faulty PSU, PSU not strong enough. Faulty CPU. Faulty motherboard. RAM not working properly. Probably more causes I don't know of.

My Setup:

Video Card: GTX 780, slightly overclocked (889 MHz > 989 MHz Base Clock). However, most times I had a black screen was when I was browsing, not when playing video games. Estimated power usage: 250 basic, plus overclocking part (~300?)
CPU: i5-750. Overclocked from 2.66 to 3.32 GHz everytime I had a black screen. I didn't tinker with voltage. Just upping the base clock speed from 133 to 166 MHz (with 20x multiplier). Estimated power usage: This link suggests around 190-220.
New CPU Fan: Scythe Mugen 4. Power estimation: Max 160 Watt. Depends on sockets, though I'm not sure what this means for my PC.
System Fan: ??

Power usage: If I use maximum values of the above: 250+220+160 = 630 without peripherals, system fan and other smaller parts. My PSU is four years old, not sure how much this matters. Though I don't see why my GPU would be functioning at max power consumption when I am browsing or when the PC is unable to start.
Temperatures are fine. <70 for CPU. <80 for GPU.

What I tried: I replaced the BIOS battery and reset the BIOS. Didn't work. I removed the RAM sticks to see if those were the issue. When I didn't use the left RAM slot the computer would start again. I thought I found the issue, considering the newly installed CPU fan was pushing against the left RAM slot. After cleaning the left RAM slot the PC was functioning perfect again.

However, today the black screen with max GPU fans happened again. The CPU fan wasn't pushing against the RAM sticks. I could quickly resolve it this time by just resetting the BIOS (which defaults the CPU back to base clocks). The RAM was also working fine afterward.

Personal conclusion: In hindsight, the problem with the RAM slot may not have been the actual cause of the original problem, but actually a second problem that arose when I was trying to fix the first problem (I was meddling with the case and fan). By not using the left RAM slot, it not only fixed the secondary problem but may have also temporarily 'fixed' the original problem by decreasing the overall power usage of the system.

I think the actual problem might be my PSU, considering I recently overclocked my CPU and installed the Scythe Mugen 4. It could also be a CPU problem because I was overclocking it.

Questions you might be able to help with:
  • Any thoughts?
  • Do you think my system might use more than 750 Watt?
  • Any advice on how to proceed? It's a shame I probably can't overclock with a 750 Watt PSU, considering I just bought a new CPU fan to keep the CPU cooled.
  • Any idea why resetting the BIOS fixed the problem the last time, but not the time before that?
6 answers Last reply
More about black screen gpu fans rotate max speed 750 watt psu problem
  1. What make/model is your PSU?
  2. That PSU should be sufficient assuming it is working properly. PSUs can and do wear out, become less effective/efficient, and die.

    Does the system perform properly with all devices running at stock speeds? If you don't know, this is where we need to start the troubleshooting process. You need a good starting point for comparison. This could simply be that some component can no longer tolerate the higher OC settings.
  3. I'm not getting the black screen with fans at max speed anymore, however today and yesterday I already had 3 or 4 blue screens with different errors each time. Someone suggest it might be a lack of voltage moving to those parts. This is with everything at stock speed. I'm thinking about just removing the Scythe Mugen 4 again and just use the default CPU fan. I don't mind buying a new part but I'm a bit for loss WHICH part I need to replace.

    Thanks for the help by the way!
  4. The Mugen does not draw 160w. It is rated to cool CPUs up to that TDP level.

    What make/model is this mobo? I suspect a motherboard issue, rather than a power issue.
  5. Thanks I didn't know. Also my apologies. I thought I wrote a reply but apparently it didn't go through.

    I use a MSI P55-GD65 (MS-7583) motherboard. This morning I had the black screen again, but everything on my computer was using default clocks. I removed the fan and that seemed to fix the issue. Haven't had problems since then. Overall I'm very confused. Not sure whether to replace my mobo or my PSU. I doubt the CPU fan itself is the cause of the instability, but I'm not that much of an expert so who knows. The PSU was fairly expensive (~140 euros with tax I think). A new motherboard would mean I would have to reassemble the whole computer, and that will probably only lead to more issues knowing my skill with tinkering.

    I might buy a cheap tool that can measure the power that my computer is consuming. Not sure how hard it is to apply that though.
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