I can't have phone extensions and modem working together

After a rare winter thunderstorm my modem will not work together with phone extensions.

I can only connect to internet by taking faceplate off my BT Mastersocket and connecting directly. But that way I can't use my internal home phone extension sockets.

If I put faceplace (to which my extensions sockets are wired) back on, my 4 phone extension sockets work (only use one anyway) but modem will not connect.

I have tried another Mastersocket that cost £5 (BT would charge £100) but still can't get modem and extension sockets working together.

Wiring of Mastersocket and extensions seems fine.

Any advice please?

[Admin]

Have you checked your microfilters?

Did the power go out or "flicker" during the storm? maybe something got fried somewhere?

[woody]

As you had this problem after heavy rain the problem could be on your extension wiring. Do you have any wiring that runs outside your house. If so there might be a break on the wiring and it as let water in and the insulation of the wires begins to break down.
As your computer works when you disconnect your extensions this points to your extension are the problem. You could start by unplugging everything from your extensions then see if you can connect to the internet. If it works then it one of the items plugged in to your sockets if this is the case plug items in one at a time and try to connect to the internet after you do each item when you can not connect the last item plugged in is faulty.
If when you have taken out the items from your extension sockets you still can not connect to internet the fault will be on your extension wiring or sockets to isolate this you will have to disconnect your extension wiring from each socket. I would suggest working backwards towards master socket and trying to connect to internet each time. If you have more than one cable connected on your interface at master socket disconnect them one at a time trying to connect to internet after you take each cable off.
Another reason could be you have gone over the ren factor each item you connect should have a ren value on it this should not go over 4 when you add them all up. This should only apply in your case if have added or replaced and item also if you have added or replaced an item recently it might not be compatible with the rest of your items plugged in.

By the way your phone could still work as yours does even if you do have a problem on your extension

Sorry its a bit long winded but tried to think of everything that could cause your problem.