ZTE ZXHN F620 Optical Network Router (ONR)

Check the light indicator on your device. 

ZTE ZXHN F620 Optical Network Router (ONR) no power light
ZTE ZXHN F620 Optical Network Router (ONR) Steady red light
ZTE ZXHN F620 Optical Network Router (ONR) No PON/internet light
ZTE ZXHN F620 Optical Network Router (ONR) Red PON light
ZTE ZXHN F620 Optical Network Router (ONR) No LAN light