PC cold boot stops during BIOS, works on restart/warm boot

[Cheshire Lad]

First post so hope I've done it all correctly.

For the past few weeks when powering up my (elderly but otherwise utterly satisfactory) PC it stops during BIOS after displaying the CPU details - image attached. Pressing Del or other keys has no effect. Pressing the Reboot button on the front panel it boots fine every time.

As the next line it would display is the memory check I wondered if it was a memory issue so I've run MemTest86+ for 1 complete pass, no errors found.

One chance event produced some more evidence. One evening after closedown, I forgot to switch the mains power off at the wall socket which I usually do. The following day it booted perfectly. so for the next week I left wall power on after PC closedown, and every time it booted perfectly. After a week of this I switched it off at the wall and the following morning it hung in BIOS. This is before memory check, before drives detected. I now usually leave the wall socket on overnight to avoid the hang the following morning.

The CMOS battery has been replaced twice.

Is this a cold boot / warm boot difference.

Whilst it's not a real problem for me as the PC is working very well, it may be a warning of something or it may just be something has changed, perhaps inadvertently by me, and needs changing back, though no idea what.

I'm reluctant to flash the BIOS with the risk of creating a brick.

Any thoughts on how to progress this?

System Configuration
Components (all housed in a generic Coolermaster Elite tower case)
MoBo: Gigabyte GA-P55-USB3
Rev.: 2.0
BIOS: Award
Version: F9
CPU: Intel Core i5 760 @ 2.80GHz
RAM: 4 x 2GB Corsair Vengeance DDR3
Graphics card: NVIDIA GeForce GT710
Internal drives:
 Samsung SSD 850 Pro 512GB ATA
 WD Black 2GB
CD/DVD writer
USB cards   2 x Dynamode 4-port USB3
      1 x 4-port USB2
PSU      650W Seasonic Focus PX-650 80PLUS Platinum, Fully Modular
Case Fan   Noctua NF-A9 PWM

OS      Windows 10 Professional, version 20H2 (Build 19042.928)

[dmdilks]

This is before memory check, before drives detected.

Understand something if you are at the Bios screen it has already check the memory. When a computer boots the 1st thing is the CPU, than the memory and than the video. If one of those doesn't check right you never get any thing on the screen.

If it is at that point it is starting to check drives. If you have any USB drives connected. Unplug them and see what happens. It more likely a drive that is causing then problem.

If you just shutting it down and not turning off the main power. The PSU will still draw power and the USB will still have power.