Problems with ADSL on a house extension

I installed Pipex ADSL yesterday and, to cut a long story short the light on
the modem flashes constantly (I believe that this means that it isn't
synchronising) and I can't connect from an extension in my study which is
approx 12 feet from the main BT box. I talked to Pipex and they told me to
unplug all other appliances from the phone circuit but it still didn't work.
They said that they would get BT to check out the line again but that if
there was no problem they would need to check their box in the house and
that if the problem turned out to be my extension wiring they would charge
me. At this point I moved the whole PC to the hall and plugged the modem
into the main BT socket to find that it connected OK.
When I had the PC in the study I had tried to connect via the telephone
extension and a long fly lead to the main BT box, neither of these would
work.
I am a fair way from our local exchange but I cannot believe that the 12
foot extension (conections in both boxes seem to be OK with the standard 3
wires connected) is the straw that broke the camel's back as phone fax and
modems (56k) work with no problems.
Does anyone have any suggestions as I have run out of ideas ???

Regards
Mike

"Mike Day" <(E-Mail Removed)> wrote in message
news:ugEub.9283$(E-Mail Removed)...
> I installed Pipex ADSL yesterday and, to cut a long story short the light
on
> the modem flashes constantly

Read the thread called "Line test failed was it kosher" dated the 17th
November and yes it does make a difference as you have proved.