Your ISP generally has a live if not email support tech dept. for troubleshooting different setups. You will need all account information ready since they will request that first when contacting them directly by phone. The operator will then transfer the call to the first tech available.
By email you would still have to provide account information there. But you would have time to fully describe your connection dilemna being seen.Calling D-Link wouldn't help there since since you would see the same problem with a different brand with the same type of router. However looking over their online support and Faq section may provide a clue.
