Teledyne LeCroy HDO4024A black screen and not booting

[Thorax]

Hey everyone,
we bought a HDO4042A in 2017/2018 and haven't really used it much in our Lab due to Covid and having more portable Scopes available.
It wasn't switched on for at least a year, when we actually needed it last week.
Now this f***** expensive scope, that has not been used more than 20 hours and is of course out of warranty, will no longer start up. Just to get a quote we'd have to pay 1700€...
We checked the webs and found this thread https://www.eevblog.com/forum/testgear/lecroy-hdo6034a-wont-boot-anymore-fixed/msg5180832/#msg5180832
so of course we changed the bios battery, but no luck.
Symptoms are also a bit different:
When the power button is pressed, all LEDs flicker on and the power supply fan, as well as the big fan in the middle of the Scope turn on.
However the fan on the PC-Mainboard does not start. Neither does the Screen or anything else. The PC is supplied with 12V, but it does not turn on.
Is there any way to start the Mainboard? Any other ideas what to do or measure?

This is probably the last hope for this scope... Our department won't invest 1700€ or 2500€ for the repair on a written off scope... I'll probably have to trash it and i wouldn't even be able to salvage it for myself due to legal reasons...

[m k]

Sell it to the friend with a firm and by it from there.

Maybe you must reset the memory behind the battery.
If there is RTC your current time is wrong, but that is not the first thing.

Is it a push button, have you tried pressing it longer?

If low battery situation is not recovering automatically there must be a procedure.

[Thorax]

Yeah, i tried different long presses and turned it on and off numerous times but nothing is happening.
All the restoring procedures on the lecroy website assume that the system is at least booting to bios and there's power to the USB ports, but there's nothing going on. I couldn't find any further service manuals or anything...

[m k]

Some PCs have a "clever" feature that the machine is not booting without a setup memory battery.
After battery is present the memory is of course corrupted and usually F1 must be pressed.

In this case the situation can be so that the computer is on but load is not enough for a fan.
It's also possible that display is special and uses some later initialized hardware.

There seems to be an old serial connection possibility.
Connect a terminal and maybe you see some text.

You can also connect a normal USB keyboard, its lights come from the other end.
What then if it responds to NumLock or CapsLock.
I'd say that in that case somewhere is a connector for active display.

E,
I found two clear power on thingies.

WaveJet
Step 1: Disconnect any probes or cables from the inputs of the scope.
Step 2: Push and hold the DISPLAY key and power on the scope.

WaveAce
Step 1: With power off, begin pushing the MATH button frequently and repeatedly. While pushing  the MATH button, power up the instrument. It may take a few tries until you can enter the scope menu.
etc.

Maybe it's a hardware only thing.
Like in PC where motherboard has a DIP switch, a push button or a pin header pair.

[Thorax]

Thanks, for all the Info. A colleague got another support tech on the line and they sent us a proposal to fix it for 1700€ which seemingly includes calibration.
My boss approved it. I hope we don't pay 1700€ for a button combo, but i'll probably never know.