Motherboard or CPU? Asus Z79-A - Red CPU_LED

[tedcblast3]

Hi guys,

I'm trying to diagnose my younger brother's computer. It's been working perfectly for the last 2.5 years until a few days ago. This system has not been OC'd at any stage.

Currently, the CPU_LED is showing red on the motherboard and every so often when powering on it shuts down within a second as if something is causing it to short?

Nothing is being displayed to the monitor from the GPU or integrated graphics.

I've followed this guide here to rule out common faults: http://www.tomshardware.com/faq/id-1893016/post-system-boot-video-output-troubleshooting-checklist.html

Other things I've tried:

- Removed the mobo from the case.
- Stripped the whole thing down to just CPU & RAM while removing all other connections(case, HDD etc).
- Tried 3 different PSUs.
- Cleared CMOS.
- Removed all RAM. Tried one/two sticks in different slots.
- Removed the CPU. Interestingly the CPU_LED remains red. This could mean the CPU is just missing though -- however, the RAM_LED doesn't show when removing all memory.

Other things of note:

- All case & CPU fans work.
- Graphics card fans work.

At this stage I'm thinking the motherboard is the problem as I understand they die more often than CPUs...could be wrong though.

I'm currently waiting for a system speaker to arrive to try and get a better diagnosis.

Any insights or suggestions are much appreciated.

Specs:

- i7-4790K LGA1150. Noctua NH-D14 Cooler
- Asus Z79-A
- GTX 980TI
- 16GB Corsair DDR3
- Corsair CS750M - 750 Watt PSU

 

[Paul NZ]

It maybe overheating. Since you've removed everything else, clean the paste off it, use a bit of iso alcohol, and reapply thermal paste

Then reinstall it, make sure its on properly

 

[tedcblast3]

It maybe overheating. Since you've removed everything else, clean the paste off it, use a bit of iso alcohol, and reapply thermal paste

Then reinstall it, make sure its on properly

Thanks for the reply Paul. I forgot to mention a CPU cooler was being used and was working(low temps) when I first built it. I've updated the specs in my OP.

I don't think heat is a problem though. The problem started occurring in the morning after it had been off all night.

 

[tedcblast3]

Update.

By chance it actually booted today...only once though. The BIOS loaded and all the hardware was recognized. CPU temps were all good too.

Unfortunately, I didn't have any HDDs connected so I could do nothing else.

I have no clue why it worked this one time but it's looking like the mobo is the problem.