I bought a used AX50 and am not successful setting it up. Is it broken?

When I switch it on, the LEDs behave as follows:

• All are green for a short moment
• While the others are green, the Internet LED turns amber for a short moment
• LEDs are turned off except for the Power LED
• Power LED remains on (green) for a long time, perhaps a minute
• Power LED blinks about eight times
• All LEDs off
• The cycle starts again.

Other details:

• My wireless devices (smartphone, PC) don't see the router's SSID.
• The modem doesn't detect any activity on the LAN port to which the router's WAN port is connected.
• When connecting a PC to one of the router's LAN ports with an Ethernet cable, the PC says that no media are connected.
• Pushing the router's reset button has no effect, i.e. no LED is switched on or off.

I did try several Ethernet cables, but they should all be good.

Are there any options for me to get the router to work?

Thanks in advance,

Bernd.