[SOLVED] Asus P8Z77-V Pro won't POST; shuts off after a half second (repeatedly)

Jul 30, 2022
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What should happen if you try to power a P8Z77-V Pro on with no CPU/RAM/video card?

Current behavior:


With absolutely everything unplugged (no CPU, no RAM, no nothing) except for motherboard power and the power switch (with the green standby LED on, indicating the motherboard has power), when I hit the power button, the power supply and CPU LED briefly come on, and then immediately shut off. After a few seconds, the same thing happens, and this repeats until I disconnect power (via the switch on the power supply).

I suspected this was a power supply problem, but I measured 24V on my power supply, and I get the same behavior with a brand new power supply.

Prior to removing the CPU, I tried removing the video card, all the RAM, using one RAM stick at a time, etc. with no change in behavior.

Background:

This computer had been working fine for a while. I put it in standby one morning, and then when I came back it was running, but I wasn't getting any video. I tried rebooting and never saw it POST. Initially, I suspected an issue with the video card or video cable, but switching cables and using onboard video made no difference.

After that, I started to suspect a BIOS issue, so I tried resetting the CMOS memory, reseating the CMOS battery (which I measured at ~3.1V), pushing MemOK , etc. I also removed the motherboard from the case, in case there was a short, but that didn't help either.

I was getting inconsistent behavior (sometimes the DRAM LED would be on, other times not). Eventually, I got into the infinite reset loop described above, and I've never been able to get back out of that loop.

From other threads I've found, it sounds like the motherboard is probably toast, but I saw at least once person claim it was a CPU issue. Is it plausible that a CPU issue would cause this motherboard to go into this bizarre reset loop?

I'm leaning towards replacing the motherboard next, unless anyone else has ideas, but I'll be pretty annoyed if it actually ends up (somehow) being the CPU.
 

Rogue Leader

It's a trap!
Moderator
A failed CPU can cause a reset loop.

Testing a motherboard with no CPU or RAM is a complete and total waste of time. You will get exactly the behavior you describe with no CPU and RAM, whether the board is good or not.

I can't say for sure your CPU is bad, and I would tend to say its not as CPU failures are far less common than Motherboard failures.

If CPU with 1 Stick of Ram won't boot to BIOS with Onboard video, and you DON'T get the DRAM fail LED then the Motherboard is likely failing. It could be the CPU, and if you could find another board to test the CPU Its probably ok, most likely its the board. The board may have a CPU LED as well that would light up if the CPU failed.
 
Reactions: ericbneverscared

Rogue Leader

It's a trap!
Moderator
A failed CPU can cause a reset loop.

Testing a motherboard with no CPU or RAM is a complete and total waste of time. You will get exactly the behavior you describe with no CPU and RAM, whether the board is good or not.

I can't say for sure your CPU is bad, and I would tend to say its not as CPU failures are far less common than Motherboard failures.

If CPU with 1 Stick of Ram won't boot to BIOS with Onboard video, and you DON'T get the DRAM fail LED then the Motherboard is likely failing. It could be the CPU, and if you could find another board to test the CPU Its probably ok, most likely its the board. The board may have a CPU LED as well that would light up if the CPU failed.
 
Reactions: ericbneverscared
Jul 30, 2022
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Thanks for double-checking my logic! I will look into replacing the motherboard next.

I've never experimented with having no CPU and/or RAM, but it sounds like that doesn't actually help my diagnosis (although I partly did it because I knew I'd have to remove the CPU/heat sink and clean all the thermal paste off, etc. anyway if I replace the motherboard).

I have never had a CPU fail, so I'm also leaning towards the motherboard being bad.

For the record, I previously tried with the CPU+1 stick of RAM in (only--and I tried multiple RAM sticks separately), and I was still seeing this same reset loop (after a bunch of inconsistent behavior I briefly mentioned earlier).
 

Rogue Leader

It's a trap!
Moderator
Thanks for double-checking my logic! I will look into replacing the motherboard next.

I've never experimented with having no CPU and/or RAM, but it sounds like that doesn't actually help my diagnosis (although I partly did it because I knew I'd have to remove the CPU/heat sink and clean all the thermal paste off, etc. anyway if I replace the motherboard).

I have never had a CPU fail, so I'm also leaning towards the motherboard being bad.

For the record, I previously tried with the CPU+1 stick of RAM in (only--and I tried multiple RAM sticks separately), and I was still seeing this same reset loop (after a bunch of inconsistent behavior I briefly mentioned earlier).
I mean bad RAM can cause the same boot loop problem, even a bad ram slot in theory. But if you have a bunch of sticks and tried a couple individually, and maybe more than 1 slot, and it still bombs, its definitely not the RAM.
 
Jul 30, 2022
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Actually, I don't think I tried using more than one RAM slot (an oversight on my part). I might give that a try before replacing the motherboard. Thanks!

Edit: tried a different RAM slot, with no difference.
 
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