System powers up only if cpu power connector isnt connected

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Nexus Radical

Nexus Radical

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Jan 29, 2015
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Hello people.

I'm having a very weird issue that is very confusing to figure out. Whenever i connect just the main power connector (24-pin) and even the PCI-E power connectors to my gtx 970, i can power up the motherboard and everything else like fans. However i wont get any signal to my monitor, which I guess is because i cant connect the CPU (8-pin) power connector to the motherboard otherwise nothing at all turns on (Even the PSU fans). This happens with both PSUs i have.

I've got two computers. Ones a MATX which is having no problems turning on and the other one (My main one) is a ATX is having the problem. Today alone i got new parts which i was hoping to fix the problem since i was having this problem with my older motherboard (MSI Z97 PC Mate). Yet still the power up problem is still persistent after trying two PSUs, Two motherboards, Two cases (Power buttons) and Two CPUs.

Here are some details you may need to help me trouble shoot.

Parts i'm trying to work together:
CPU: I5-4690k
Mobo: MSI Z97 Gaming 5
GPU: MSI GTX 970 4GB
PSU: Cooler Master B-series V2 700w
RAM: Corsair 2x4GB Kit Vengeance DDR3

What used to work but no longer does:
CPU: I5-4690k
Mobo: MSI Z97 PC Mate <(The Change)
GPU: MSI GTX 970 4GB
PSU: Cooler Master B-series V2 700w | EVGA 600B 80 Plus Bronze
RAM: Corsair 2x4GB Kit Vengeance DDR3

What does work in my second computer and have been using for spare parts:
CPU: i3-4170
Mobo: Asus H81 chipset (No sure on exact model , got it built for me)
RAM: 2x3GB Corsair (Unsure on model, got it built for me)
PSU: EVGA 600B 80 Plus Bronze | Cooler Master B-series V2 700w
GPU: MSI R7 250


Thanks in advance!
 
Solution
Onus
You MUST put the motherboard on standoffs (or raised bumps). If the holes in your case were not properly threaded (e.g. Coolermaster), torquing a screw into each hole first should allow the standoffs to go in easily.
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Onus

Onus

Titan
Jan 27, 2006
37,037
12
89,965
I had this happen to me when my motherboard had popped a VRM. You've tried two boards though, so hopefully that is not the case. There could be a [near] short in another device needing 12V. Try your low-powered graphics card in the problem system.
Disconnect everything not needed to POST, including all drives. If it posts, power off and retry after connecting each device, one at a time. This may identify a problem component.
 
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Nexus Radical

Nexus Radical

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Jan 29, 2015
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Same as before. The system failed to start up with the CPU 8 pin connected but was starting things up with just the 24pin.
Both cards work on the secondary computer.

I should mention that when connecting the 8pin. I have to remove the 8 and 24 pin and then reinsert the 24pin to get anything to power with just the 24pin.
 
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Onus

Onus

Titan
Jan 27, 2006
37,037
12
89,965
What's really odd is that you say this happens on multiple motherboards...

Are the motherboards mounted on standoffs (or raised bumps, but not both) in the case?
I would try building outside of a case, and see what happens. For a PSU not to turn on suggests a short.
 
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Nexus Radical

Nexus Radical

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Jan 29, 2015
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Not on standoffs. It was way to hard and couldnt do it with my case. I've got small screews that connect to the case going through my motherboards 6 holes. I've been building for about 2 years. So im not really sure if this is a bad move.

Okay, ill try on top of my motherboard box. Probably the safest option i have. Ill report back in less than 15m. Maybe about 10m.

Cheers.
 
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Nexus Radical

Nexus Radical

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Jan 29, 2015
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IT WORKED!!! This gives me hope. All i had connected was the 8pin this time and the 24 pin, R7 lower end card, ram modules and the CPU fan. So the cause was the screews on the board which mounted it to the case?
 
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