HP ProDesk 600 G2 looping on/off before POST screen after BIOS reset

[swaaye]

I went into the System UEFI setup and reset to defaults.  Upon restart the machine began an endless cycle of powering on and off.  The HP splash screen appears only for an instant before it shuts off and turns on again.  I can't get into the BIOS again.

Clearing the UEFI by motherboard reset button slightly changes behavior by causing an initial longer startup, but then it resumes the power on/off looping.

Password jumper was missing.  Replaced it but no effect.

I noticed before resetting to defaults that the system UEFI is a 2016 version so fairly old.

Any ideas?  Is it history?

[CF4]

Hi

Ideas?  Yes;   Sensible solutions?  NO.

https://support.hp.com/us-en/document/c02693833

Turn off the notebook.
Plug the notebook into a power source using the power adapter.
With the notebook off, press and hold the Windows logo key and the B key at the same time (WinKey +B).

NB: On some notebook models, it might be necessary to press and hold the Windows logo key and the V key (WinKey +V).

While pressing those keys, press and hold the Power button on the computer for 2 to 3 seconds, and then release the Power button but continue to hold the Windows logo key and the B or V key until the HP BIOS update screen displays or you hear a beeping sound (usually 8 beeps).

Please try a Hard Reset
This is valid for most notebooks, and some desktops.
Press and Hold the PWR off button for 4 seconds to force a PWR off.
Unplug from the wall.
IF you see a battery compartment door, then your computer has a removable battery.

IF NOT then you do not have a removable battery.

Remove any removable battery.
Press and hold the power button for 15 seconds to complete the reset.

(Re-insert any battery you removed).

[DGroves]

try removing the Hard drive(s) and see if you can get a no bootable device message. if you do is it stable IE- no rebooting unless you do it. if so then the OS on the drive or the drive itself is the issue

if you still have a reboot issue, try swapping ram module locations, or running with less ram

http://h10032.www1.hp.com/ctg/Manual/c04831203

http://h10032.www1.hp.com/ctg/Manual/c04844074

https://support.hp.com/us-en/product/hp-prodesk-600-g2-small-form-factor-pc/7633319/manuals