How to get Internet over Powerline to work?

Hello


Setup
=======

I have deal with my ISP where they supply both internet and television
over ADSL. They have supplied me with a modem, which has two ethernet
exits, one for the Decoder (TV) and one for a PC (Internet).

The problem is that the modem, computer and tv decoder are all in
different rooms of the house, and neither can be moved to another room
(I know that this sounds like an exam question!).

So I have tried to connect both exits on the modem (TV and PC) to two
seperate "PowerLine Plugs"/"NetPlugs". In the other rooms, I have a
power line plug connected to my computer, andin the other room I have
another power line plug connected to my tv decoder. So it looks like
this:


MODEM
| |
(computer PL)-----PL PL........(TV Decoder PL)

PL = Powerline Plug

BUT it seems that when my internet works, the tv dosent, and when my
tv works, my internet either is super slow or dosent work.


Question
========
Is this because you can not use multiple Powerline Plugs in the same
apartment? Does the TV signal interfer with the PC signal? How can I
fix this?

Thanks

Zach