Wish it was in the posts here.
I can't find a few details. I may have missed them. The router make, model, version, firmware and if you've tried another router.
I've seen swapping a router fix the above but most owners will say that everything else works and not do that. It could be cables but the few times it was, the cables were made by the owner and the other times the cables had obvious damage.
Sorry but I can't see the cause in the posts so it's time to tell a little more and then start changing parts.