The following should be undertaken when troubleshooting why a device has gone offline with a suspected communications issue:
Fixed Connection (LAN)
If using DHCP – can other devices on the network obtain an IP address?
If using a static IP – has your device been assigned the correct static IP and are the DNS server settings correct?
Have you followed the steps in How do I connect my device to a LAN network?
Wireless Connection (Wi-Fi)
Follow the steps in the Fixed Connection (LAN) section above additionally:
Has your device been configured with the correct Wi-Fi SSID and network password?
Are the Wi-Fi antennas securely connected to the device?
Cellular Connection
Is the SIM card securely installed in the device?
Are the cellular antennas securely connected to the device?
Is the device configured with the correct APN details?
Is the SIM card active and does it have a valid cellular data plan?
Have you followed the steps in How do I connect a cellular-enabled device to a 4G network?