HP CP5525 will not finish initialisation / initialization

[PeterCalrec]

Hi All,
I hope someone can help me with my laserjet that is now a door stop....

I came in after the weekend and the printer wouldn't wake up. When I printed to it via our network, no flashing data light, no print, unresponsive front panel buttons.
I pressed the power button and it closed down, then pressed again to restart.
The display shows: HP 1/8 to 8/8, then Checking hardware 1,2,etc., then Initialising 1,2,3, etc.
Initialising (initializing?) just keeps counting up for 1000 plus counts and never finishes

I have tried:
a full power down and drain - holding the power button for 30 seconds+ with no cables connected. Power on with no network cable. New firmware, which changed the boot screen, but not the outcome - still initializing. Going into the preboot and disabling checking on various things. A partial disk clean, but nothing seems to make any difference

When it is initialising, it hasn't got as far as enabling the web interface so no access to the printer at all remotely, only via 'press cancel when all 3 leds are lit' as per the manual

Any ideas are welcome to get this printer working again
It is long out of warranty....

Regards,

Peter

Forgot to say, the 'print engine test' works when I press and hold the button in the air vent - a perfect A4 sheet with coloured lines

If I have tripped over etiquette anywhere, then I apologise in advance