[SOLVED] Why 2 good MB's won't POST - with same error?

[bsmith_52]

The audio stopped being recognized by Ubuntu in my Gigabyte Z390 Aorus Pro MB – with used Intel 8400 CPU – but was still working. I ordered a replacement MSI MPG Z390 Gaming Edge MB. New MB would not POST – got stuck on pre-POST Bad Memory check. Called MSI. Concluded board bad - believed memory was good as it was from working system - so started RMA for refund.

During this time, “something” happened to 2 other PC’s – the Lenova laptop was not able to boot into Ubuntu (dual boot) – Wondows 10 and hardware unaffected but Ubuntu and/or EFI partition trashed. My AMD 3700x build all of the sudden was unable to POST– it died on pre-POST check at “Boot” (on-board LEDs). A CMOS reset fixed this problem – no further issues here (BTW, all 3 computers were on power line conditioner).

Before sending MSI board to manufacturer, I reinstalled Gigabyte MB. Formerly working board was now also stuck on Bad Memory. Checked memory with 4 passes (3 Hrs 25 min) with memtest86. Passed with 0 errors. Rebooted with checked out memory. Same Bad Memory error.

Is there a way to test for bad CPU? Anything else that I can check?

Hardware:
PSU: Corsair RM750i
Memory: G-Skill Ripjaws 2133 DDR4 2x8gb FA-2133C15D
Motherboard 1: Gigabyte Z390 Aorus Pro
Motherboard 2: MSI MPG Z390 Gaming Edge
CPU: Intel i5 8400

 

[Flayed]

Is there a way to test for bad CPU? Anything else that I can check?

You can look to see if any pins are bent

 

[bsmith_52]

I will check. I thought that I was careful. But who knows?

Thanks