New modem installed today.  Congigured to ISP ok.  Set up wifi ok.  Connected 4 x Ethernet clients ok.

After approx 7hrs all 4 Ethernet clients went down. 
Rebooted modem, Ethernet clients initially came up but after approx 10-20 seconds all went down again

Unplugged all Ethernet ports, replugged.  All Ethernet clients came up & went down again adfter approximately 10-20 seconds.

Reset X20, recreated ISP connection, wifi.  Each ok.  1 Ethernet client came up for 10-20 seconds then down again.

Wireless is ok, both frequencies.

Date & time set correctly but not reflected in any logs.  All logs start Thu Jan 1 09:30:40 1970.

checked firmware, up to date, no alternative offered to dowload

Need help ... How do I get the 4 Ethernet ports up & stable?

Ps tried to load logs but upload failed.