XS708E stuck at boot / fan speed max / orange PWR-LED blinking / no Uplink

Hi peeps!
I need your help.

Bought two second hand XS708E (v1, not v2!).
One is good, the other one won't finish booting.
- Power-LED ist blinking orange/amber.

- Fans run at max rpm / full speed.

- Ports aren't initialized, and won't get uplink

The factory reset button shows no function: not 3 seconds, not 5, not 10, not 15.

Even the "trick" to push factory reset and THEN plug in power won't work.

Any ideas?
I'd even go out and sing Last Christmas to him.

Cheers - and thank you SO MUCH in advance.
Kai