To eliminate variables, you should remove your router from the equation. Plug your computer directly to the modem and see if that solves your problem. If it does, then you may have an improperly configed router or it may just be flakey. I've had numerous brand-new routers go bad very quickly.
When troubleshooting anything on the network, always look at the physical side/hardware FIRST. IP v6 is not your issue. If you can connect period, your ip settings are correct unless you are seeing an ip address conflict. But, as stated above, plug ONE machine into the modem and bypass the router and that would be an impossibility. You are just fine with IPv4 fyi..
Remove anything you don't absolutely need in order to connect to the internet. Make it barebones and try to get it to work.
Are all computers/devices on the network having the same issue or just your desktop?