Wireless-N 300 Modem Router(DGN2200) - CONNECTION PROBLEM

Hello everyone. I have a modem with the model specified in the title: N 300 Modem Router(DGN2200). I did the settings reset, then I connected the antenna cable into the antenna slot and I have the following problem. Strangely, with the PC, I can only connect in wifi mode (it does not recognize the Ethernet connection. It says, “no internet access”). But the real problem is when I try to connect with other devices, like my cell phone for example. It recognizes wifi but even here it reports “Unable to access the internet” despite being connected to the modem. I don't understand where the problem is... Can anyone help me?