Can you test powerline devices using your computer instead of Sky box? What's the IP address obtained on computer and Sky box when testing seperately?

Your router suppports IGMP function? Is it enabled?

Eduardo wrote Please Can someone confirm the firmware TD-W8980_V1_140919 is applicable for TD-W8980_V1 ? The note of the newest firmware says: "For TD-W8980N(UN)_V1" and I can´t find out what N(UN)...

You are sure MAC address you put in is correct. Follow this guide and allow a specific website to see if it works. http://www.tp-link.com/en/article/?faqid=453

In facotry default settings, it is in bridge mode. You can just simply reset it. But the problem is that you cannot access internet in bridge mode except that you build a PPPoE connection on PC. If...

If it is not compatibility issue with your ISP, I think your M5350 is not working properly. What's the band supported by your ISP?