HP Elitebook 840 G5 strange behaviour, need ideas...

[Stefan Steff]

I finished my work for this year, so I'm free until January 6th.
My last task it's unresolved and I'm looking for ideas for the return in January.

So what's about...
This laptop is booting in 3-4 seconds has no password and every voltage is present. So far so good.
My problem is that it doesn't boot from anything. !...just stays with a blank screen(backlight only)
No USB boot (in fact partially no boot...), no PXE boot nor boot from M2.SATA or NVME...crazy...
The Ventoy USB (EFI) boots in the menu system but after selecting one of the ISO (like a simple Memtest86+) I get the blank screen.
When installed the M2 drive restarts a couple of times and then stuck on "Preparing Automatic Repair"

What I did:
- Updated to the latest BIOS 1.29.01 (updated from BIOS , Main->Update System BIOS->HP.com).
- Downgraded to 1.21.0 (a 2023 BIOS version).
- Writing a brand new BIOS firmware with SVOD4(tried rewriting both, in pair with EC and get rid of Endpoint error)
- Changing RAM to a tested one.
- Installing an M2 drive with Windows 10 64bit from a working laptop.
- Tried Reset Factory defaults and Security defaults.
- Disabled Secure boot, Enabled/Disabled Legacy boot.
- Disabled HP Sure Recover
- Disabled/Enabled Fast Boot

I'm out of other ideas...
I thought it might be a hardware problem but I don't know where the problem could be.
I'm willing to try any idea I haven't tried before.

Thanks!
S.S.

[mcplslg123]

Very hard to suggest anything valuable without having the mb on table in this particular case.
You've taken almost all the steps.
Have you inspected the board for corrossion/liquid spill under microscope?
Even if you have done,try inspecting again more slowly and closely-may give you a clue.

[Stefan Steff]

Very hard to suggest anything valuable without having the mb on table in this particular case.
You've taken almost all the steps.
Have you inspected the board for corrossion/liquid spill under microscope?
Even if you have done,try inspecting again more slowly and closely-may give you a clue.

Yes I haven't seen any visible liquid damage...I have to put the board under microscope and take a closer look. Thanks!