PC won't boot, red CPU LED lights up. Asus M5A99FX Pro R2.0

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Shenflie

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Nov 4, 2015
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Hello Tom's Hardware!
I have the following problem:
About 2 weeks ago, my computer would not boot up. There was a CPU led on my motherboard lit up red.
Tried everything, would not POST in any setup.

After giving up for the day, tried to boot it up the next day, and it did. Used it for the rest of the day without issue.
However, after turning it off for the day and trying again the next day, it did not boot, again the red CPU LED.

Taking everything off the motherboard, including CPU, cables, GPU etc., and putting everything back, it still does not boot. However, if I do all that and take out the motherboard, then put everything back, it boots. That's worked twice now, and it keeps working for around 3 days. Turning it off at the end of the day, and turning it on at the start.
But then it again shows the red CPU LED.
EDIT: Regardless of the red mobo CPU LED staying on, all the fans work.

I am at a loss.

My specs:
Asus GTX 760 DirectCU II OC
AMD FX 6300 Black Edition
Corsair CX600M PSU
Cooler Master Hyper 212 Evo CPU Cooler
ASUS M5A99FX Pro R2.0 Motherboard
Corsair Vengeance 2x4gb 1600 mhz RAM

Thanks in advance for any help! :D
 

Shenflie

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Is there a way to test the PSU? I do not have access to a different PSU.
 

Shenflie

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I will try to get the parts required to test it soon, but in the meantime, I forgot to mention that the fans work, regardless of the LED situation, does that matter at all?

Also, is it possible for a PSU to sometimes work? Especially considering it worked for a while after taking everything out.
 

gregvibe

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Oct 9, 2015
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if the diagnostic cpu led is red then something's wrong with the cpu. you can remove the cpu and reinstall it and put thermal paste. you can also try with another fx cpu
 

Shenflie

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I followed This guide to test the 24-pin mobo connector, and everything is at it should be, except the Gray Power OK wire voltage is too low.
Using a PSU that as far as I know works properly, the Power OK reading is the correct voltage.

This points to a problem with the motherboard, or maybe the PSU and the mobo?

*I did the test wrong at first*
 

Mark_1970

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Nov 14, 2015
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Sometimes a fingerprint oxidises the contacts on the cpu or some paste is fouling it. clean with isopropyl alcohol . could be any of the things said previous too. just another thing to look for :)
 

Mark_1970

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Nov 14, 2015
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The 4/8 pin eps is powering cpu
 

Shenflie

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Tested the 8 pin, 12.14v.
 
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