My computer has internet when I plug an ethernet cable from router and when I plug directly from modem I have no internet

[Roywastaken]

My computer has internet when I plug in an ethernet cable from router and when I plug directly from the modem I can't connect to the internet.

 

[BuddhaSkoota]

You may need to reboot both the modem and computer when you move the cable.

This because the router's MAC address is registered as the IP recipient, and rebooting makes the computer the registered device.