PC Won't boot, fans start and stop

Hi there

To begin with my system has been running just fine, I had been running the following specs for the majority of the past 9 months other than the parts which I stated their age, else rest was bought 9 month ago.

Gigabyte Z68AP-D3 Intel Z68
ATI 5850 (roughly 3 year old)
G.Skill Ripjaws 4GB X2
I5 i2500K @ 4.4ghz
OCZ ModXStream Pro Power 700 Watt (just over 3 year old of 24/7 use)

I recently decided last week to upgrade my GFX card to a ATI 7950. Everything was up and running fine, as I decided then to take it for a test spin on Witcher 2 and after about 20 minutes in my system just completely shut down. When I tried booting it up after this, all that would happen is the fans would go on full speed but no screen would show. I doubled checked the DVI cable and such also the PCI-E power cables for the GFX making sure they were securely in and not loose but none of this helped so I then ended up deciding to try reset my CMOS, which did not help either.
So after all this I then decided to dismantle my system removing the GFX card first just to check if fans would go back to normal after unplugging this but that made no difference so I continued to unplug everything on my motherboard except 1 RAM chip,cpu fan, the ATX 4pin and the ATX 24pin power cables, which I left both plugged in. I attempted to start up my system again but still no luck, the fan(cpu) was still going full speed, so I ordered myself a new PSU - Seasonic SS-650RM 650W.

Okay so when I got my new PSU set up, I gave it a bash and this time I could actually see the screen again when starting up but it would only go as far as the motherboard screen then it would just shut off and loop again, the fans also were back to normal speeds now though. I ended up trying to reset the CMOS again, I just was trying anything at the point, but this would still not change the outcome, which it was still going into a loop of shutting down at the motherboard screen. So once again I unplugged everything, similar scenario as before leaving 1 stick of RAM, the ATX 4 pin and ATX 24pin plugged in(i tried plugging and unplugging the CPU fan here). Now instead of the system actually staying powered on for a period of time, it would start the PSU and CPU fans for briefly 1-2 seconds then stop. I tried removing that 1 stick of RAM and booting with 0 sticks but that didn't make a difference either.

I did a thorough check over the motherboard, as far as I can tell nothing looks damaged or anything like that and had a quick check over the CPU, which looked perfectly fine also. On top of that I tried multiple kettle cables just to make sure.
I honestly have no clue what the problem could be if it's something wrong with the motherboard or CPU...and I don't have a spare socket 1155 mobo or CPU laying around either, so I can't separate those.

So yeah if anyone has any recommendations for me to try, would be much appreciated. I'm contemplating on whether the issue is the CPU or mobo, or maybe it is both?
3 answers Last reply
More about boot fans start stop
  1. Have you tried re-applying thermal paste ? Use silver only.
  2. Also is that CPU overclocked ? i5-2500K is stock at 3.4ghz not 4.4ghz.
    Overclocking makes systems unstable and require more cooling power and more power from PSU.
  3. Yea I have my i5 overclocked to 4.4ghz, always had it on that. I managed to solve the issue by replacing the motherboard, the CPU is still working perfect.

    Thanks anyway.
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