Thursday not so good!

Went into work as usual and opened up. Switched on all pc's we normally use each day. Come to registering the first mot and can't get internet connection?

I move to my own pc and behold I can't get internet connection there either!

I ring the service provider and they "Check the line" over the phone and tell me nothing is wrong?

I advise them that the wireless box operating light is RED when its normally GREEN. The guy on the phone says remove your filter and plug the phone line directly into the main box on the wall. Does your phone work okay! Yes. Okay your filter is the cause. I could not get hold of a new filter. The boss is away on holiday but we managed to contact him and he ordered a new filter off Amazon yesterday. This morning we entered the garage and swiched on all pc's and by some miracle the internet is up and running again. The filter arrived in the late morning and is still in the sealed packet unopened.

The moral of the story...

Your line checks out okay but your filter is faulty???

What actually fixed the fault?