The easier thing to do is to kick off with some troubleshooting first of all as this will allow us to spend our time on the specific area causing the issue.Firstly please go to your modem, take the network cable (RJ45 plug) which goes from the modem into the Devolo dLAN plug, and plug it into your laptop. Please then turn off wireless on your laptop, and check the internet is working, once we know the internet is working view the cable plug it back into the dLAN plug.
Secondly if the above works ok, take the same laptop and go to the lounge, and take the network cable from the dLAN plug and plug it into your laptop. Once more check the internet is working on your laptop, you may wish to do a speed test using www.speedtest.net this will show you how well the dLAN plug is performing (it should be within 20% of what you get by running the same test from the PC in your study).Next I need to review the results you get from the two tests above.If both tests are successful its looking like an issue with the DVR\TV configuration, if the issue is with the first test it points to a fault network cable\modem setup, of if the second option fails it may be faulty wiring \ noisy mains causing interference.
I will aim to log back on later this evening to review your progress.