"Ethernet" doesn't have valid ip configuration

I've posted this here before but not much helped. This issue prevents me from connecting to my internet on my desktop pc, usually happens once a month and solves itself but this time it's been 2 days and nothing is working. I have tried everything to fix this and nothing seems to work. My desktop is connected to my standalone router with an Ethernet cable. Please help :(

Edit: each time I press the windows diagnose on it sometimes it changes like right now, I just got your broadband modem is experiencing connectivity issues. It's only my computer that is not getting internet.

Edit: now it is also telling me the default gateway is not available. There so many issues I don't know what to do......