Question PC turns on only when CPU is not installed

Sep 5, 2020
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I have 8700k and z270 mobo for about 2+ years. one day my computer shut off out of the blue. When i tried turning it back on, it would turn on for a brief second and turn off.

Tried troubleshooting by taking off components and booting, figured it was a mobo problem, contacted Asus they sent me a z390. Installed everything same problem... Installed just CPU + Mobo, same problem (no ram, VGA, hard drives)

Figured it might be something else, got a brand new PSU, tried It, same problem. Paired the PSU with a whole new z390 mobo, with just CPU, same problem.

Last night i tried booting the computer with just the motherboards without CPU, the PSU would turn on with case fans spinning for about a good 10 seconds, and reboot, with motherboard warning lights saying no CPU connected...

Do i have a bricked 8700k??
 
Sep 5, 2020
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Did you also try to boot without RAM or with only one ram stick ?
Ya, been reading quite a bit of material, to clarify - after getting the replacement mobo (and even before), i would have the mobo and just the CPU, no ram, no VGA, no Sata. I would only connect the motherboard + CPU power connectors to the PSU. And only a on/off switch from the case

The computer would still only turn on for a brief second and shut off, i can tell from the PSU fan and case fans.

Like i said the only time i have been able to turn on the computer for longer than a second is when i have only the mobo connected to power and case, without CPU

I been building computer for more than 20 years and have never seen such a problem before, and have never had a bad CPU... but i have practically switched out all the parts and tested with just PSU, mobo and CPU without anything else
 

Grobe

Distinguished
Hm - an odd case you have.

I agree to your first post, it seems like it must be a faulty cpu. Having three broken motherboards are unlikely. I think you can only know by getting a new cpu - or maybe you can find a used one for a low price just for testing.
 
Sep 5, 2020
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Unfortunately don’t got another compatible CPU to test with, thinking i might just wait for the new ryzen for a complete new build... maybe..

But to confirm, the computer should be able to boot up (all the fans spinning and all) with just mobo+CPU correct? Even if i don’t have CPU fan connected
 
You will also need a cpu cooler and ram installed.
Most motherboards will not start if they do not detect that the cpu cooler fan is spinning.
Without a display adapter and a display, you will not see the bios.
 
Sep 5, 2020
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You will also need a cpu cooler and ram installed.
Most motherboards will not start if they do not detect that the cpu cooler fan is spinning.
Without a display adapter and a display, you will not see the bios.
Understand that i won’t see bios, but the computer would at least turn on right, with PSU fan spinning.

Instead I get a clicking sound in the PSU and fan spins for a second then turns off completely
 
Understand that i won’t see bios, but the computer would at least turn on right, with PSU fan spinning.

Instead I get a clicking sound in the PSU and fan spins for a second then turns off completely
The motherboard will not start without detecting that a fan is plugged into the cpu fan port.
That is for your own protection to not damage a processor.
 
Sep 5, 2020
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Can the motherboard differentiate between a normal case fan VS cpu fan? I hooked up a normal case fan to cpu fan plug still the same thing
 
Can the motherboard differentiate between a normal case fan VS cpu fan? I hooked up a normal case fan to cpu fan plug still the same thing
Not that I know of.
But it certainly would fail to start if there was no cpu present.
If you had a cpu present and no cooler, then possibly it would start, but the cpu would heat up in a matter of seconds and shut down.

Why not put it all together?
cpu, cooler, ram, monitor attached to the integrated graphics adapter.

It is very rare for an intel processor to fail.
Another possibility is that you may have damaged a socket pin if you were not careful dropping in the processor.
If you smooshed the cpu around to seat it, you likely bent a pin with unpredictable results.
 

Turtle Rig

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Jun 23, 2020
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There is no doubt the CPU is dead. Unless its the video card 🙏😲Also as the guru said most current mobos won't let computer turn on without detecting a CPU fan. Also try at least one stick of RAM. If you have tried a different video card as well then its the CPU no doubt. It is a process of elimination my friend. 💯🤷‍♀️☮♻
 
Sep 5, 2020
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Geofelt, the reason I’m not putting everything together is to go through the process of elimination.

I just tried it again, new PSU, RMA’d z390, 8700k with 4pin noctua fan on the CPU fan slot.

When i turn it on, PSU would make a click sound and spin for maybe half a second along with the noctua fan, before everything stops, exact problem before I rma’d the motherboard.

The only way to actually turn on the computer is when i take out the CPU, the computer would go into a boot cycle every 5 seconds and the motherboard troubleshooting light would indicate it cannot detect a CPU
 
Sep 5, 2020
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If you do not have a cooler mounted to the processor, the processor will heat quickly and shut down almost immediately.
I get that, but i also feel like there’s a difference between shutting down in a few seconds due to overheating VS PSU clicks for a split second before everything dies and goes quiet again

like the fan literally doesn’t even gets fully powered up to spin. They move by maybe a few millimeters before losing power
 
I get that, but i also feel like there’s a difference between shutting down in a few seconds due to overheating VS PSU clicks for a split second before everything dies and goes quiet again

like the fan literally doesn’t even gets fully powered up to spin. They move by maybe a few millimeters before losing power
You might be right, but you are risking permanently damaging your processor trying to run without a cooler.
 
I have 8700k and z270 mobo for about 2+ years. one day my computer shut off out of the blue. When i tried turning it back on, it would turn on for a brief second and turn off.
8700k and z270 are not compatible. There's no way they could have been working together at all.
Are you sure it's 8700k? It might have been some other cpu. 7700k - for example?

they sent me a z390. Installed everything same problem... Installed just CPU + Mobo, same problem (no ram, VGA, hard drives)
Again - if it's some other cpu (compatible with z270), then it will not work with z390.
 
Sep 5, 2020
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8700k and z270 are not compatible. There's no way they could have been working together at all.
Are you sure it's 8700k? It might have been some other cpu. 7700k - for example?


Again - if it's some other cpu (compatible with z270), then it will not work with z390.
Sorry my bad it was a z370, asus RMA’d a z390
 
Sep 5, 2020
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You might be right, but you are risking permanently damaging your processor trying to run without a cooler.
Fair, thanks for the call out. I did some searching around it seems some people even risk it and boot the computer into windows a few mins without a fan, definitely sounds silly and risky to your point

tho my problem at hand definitely feels like something else is wrong :(
 

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