@Xaimond,

If you have already confirmed that you are connected to the internet when using an Ethernet cable connected directly from your PC to the router and everything seems to be working; I would follow these steps on your Archer A7 to see if this will reconnect the router to the internet.

From the UI for the Archer A7:

Click 'Advanced' at top

then,

Click 'System Tools' on Left Sidebar,

then,

Click 'System Parameters' on Left Sidebar that opens,

lastly,

Change the 'Port Negotiated Speed' to "100 Mbps Full Duplex"

Let me know whether or not this allows your router to connect to your network again.