[SOLVED] Computer Only POSTs after flicking PSU switch on/off - CPU fan doesn't work

[lordy16]

Hey all!

I've been lurking for a while as I've had tons of trouble with this build and I just can't seem to get to the bottom of what the issue is.

Here are the specs:

Motherboard: Gigabyte Aorus b450 Pro WIFI (originally MSI b450 Tomahawk)
CPU: AMD Ryzen 3700x
RAM: 2x Crucial Ballistix 16GB 3200mhx CL 16
GPU: Power Color Red Devil 5700 xt
Storage: Intel 660p M.2 2280 2TB NVMe PCIe SSD
PSU: Seasonic 650w Gold 80+
OS: Windows 10 Pro 64bit

Outputted to a pair of Dell 27" monitors using Display Ports + one HDMI out to a television

I have reviewed all the options inside the Sticky Thread to no avail.

The symptoms:

• Audio Crackle that has recently disappeared but still shows up from time-to-time, especially with the HDMI out to the television (I've changed all three cables as well as the USB cable from the Focusrite 2i2 monitor into the PC - reinstalling the Focusrite drivers helped the crackle, but it still shows up)
• With the old motherboard, the computer would not find the M.2 drive in the BIOS on boot, forcing me to flick off the power switch on the PSU, then back on. The m.2 would then be found and boots Windows per usual
• During heavy gaming load, the computer shuts off to black without warning. Happens once every two hours or so while gaming (Borderlands 3).
• With the new motherboard, the system simply doesn't post (no BIOS screen) until I turn on-off the PSU, sometimes a few times. Sometimes, the system doesn't even start up at all, just clicks straight off with a brief flash of light and shuts down again.
• I can't restart the system as restarting will force me to flick on-off the PSU to get it to post normally.
• The CPU fan starts up, but then stops. I looked in the BIOS and noticed that the temperature reading is -55 celsius, which I imagine is the lowest it can be. I'm assuming its reading is telling the CPU fan to turn off, instead of the fan not working - I even plugged a case fan into the CPU fan slot and stuck the CPU fan into a sys_fan slot, in which the CPU fan now runs and the case fan does not.
• XMP RAM profile is reset on restart --> used the BIOS XMP profile setting to turn 1200mhz to 1600mhz per stick and it reverts back to 1200mhz upon restart.

Things I have tried (in order):

• Double checked the seating of the motherboard and wiring - Nothing.
• Updated the BIOS and all drivers - Nothing.
• I reseated the RAM, tried one stick at a time, etc. Nothing was exposed as an issue.
• I sent back the SSD (same model/make) - No change.
• I've replaced the Motherboard from the MSI b450 Tomahawk to Aorus b450 Pro WIFI - Had different symptoms (CPU Fan not working, sometimes needed to flick the PSU on/off multiple times)
• I sent back the PSU for a new one (same model/make) - No change.

I'm really clueless as to what I should do next. Is it really the CPU? When changing the motherboard and reapplying the CPU chip + heatsink, I double-checked the pins to ensure nothing was wrong - no bent pins at all.

I had to return the first CPU chip I got from Microcenter and I'd hate to have to RMA this one to AMD when I don't truly know if it's the problem.

Please help! I've been stressed trying to get this new machine to work for weeks and I'm dying to have the peace of mind that I can trust this computer to not randomly crash out of the blue & not go through the PSU switch on/off multiple times every day to get it to start up.

Thanks so much in advance, I cannot tell you how much I appreciate your help!

 

[lordy16]

After a bit more tests, I'm leaning to the CPU's temperature sensors being wonky, which would explain the random gaming shutdowns.

Would that also explain the m.2 SSD not getting read on start up & a reset of the power (turning the PSU off, then back on) in full allowing it to be found again?

Any ideas would be a huge help, thanks!

 

[lordy16]

Quick update. Ran User Benchmark:


UserBenchmarks: Game 109%, Desk 124%, Work 115%
CPU: AMD Ryzen 7 3700X - 88.5%
GPU: AMD RX 5700-XT - 118.2%
SSD: Intel 660p NVMe PCIe M.2 2TB - 244.8%
RAM: Crucial BLS16G4D32AESB.M16FE 2x16GB - 73.3%
MBD: Gigabyte B450 AORUS PRO WIFI

Ram is low since the BIOS doesn't remember the XMP profile = 2400mhz instead of 3200mhz.

Is this simply a temperature sensor problem? Is that a CPU or motherboard issue?

 

[lordy16]

I CAN'T BELIEVE I SOLVED IT!

The problem was a Display Port cable. Unreal.

One of the two cables from my monitor had the 20-pin power, which was adding power to my motherboard via the GPU (I noticed the LEDs were still on after shut down). Here's a video that did it for me:

View: https://www.youtube.com/watch?v=6s1cMwzesZI


This was frying the motherboards and causing all issues. Unreal.

I swapped out the cable, replaced the motherboard, and everything is working perfectly.

I'm sure someone else will have these same issues and I highly recommend checking the Display Port cables - try HDMI as a test or see if LEDs stay on despite the power plug removed from the motherboard.

I'M SO HAPPY RIGHT NOW.